Terrorism has been of great concern in the modern world for over a century now. Several strategies have been developed and implemented in order to counter terrorist activities and undo the harm caused by terrorist organizations. These efforts require to have a clear understanding about different types of terrorism in order to increase their effectiveness. This review study contributes to the efforts in understanding different types of terrorist organizations through a “motivation-based model.” Three different types of terrorist organizations were identified through a systematic review of relevant literature and examples of terrorist organizations under these types are examined in this study. A discussion on improving our understanding of the typologies of terrorism concludes this review study.

Classification, as an operation in science, refers to “the objects or events of a given set are grouped into two or more subsets according to the perceived similarities of their states on one or (more frequently) several properties; subsets may be successively grouped into subsets of wider extension and higher hierarchical level” [1]. Based on this understanding, the concept of terrorism has been classified previously by different institutions and authors in different ways. The FBI, for instance, makes a two staged taxonomy of terrorism as “International” and “Domestic” based on where it occurs [2]. Safarova et al. [3] takes a different approach and classifies terrorism as political, informational, economic, and household (domestic) terrorism based on ultimate goals of the terrorist activities. Martinet al. [4], makes a broader classification and focuses on the structures and characteristics of the terrorist activities and classifies terrorism as; new terrorism, state terrorism, dissident terrorism, religious terrorism, ideological terrorism, international terrorism, criminal-dissident terrorism, and gender-selective terrorism.

On the other hand, Lizardo et al. [5] provided a broader approach in classification of terrorism by taking the historical change (since 1870) of world systems into account. They identified three different types of terrorism:

1. Type 1- terrorism performed by core actors against core governments,
2. Type 2- terrorism activities arising in the periphery and semi-peripheral sections of the world and targets the local governments and
3. Type 3- terrorism activities carried out by semi-periphery-based groups towards core target throughout the world (transnational) (see [6], for a broader discussion of world systems theory and explanations of core, peripheral and semi peripheral sections of the world).

All of these studies, by taking slightly different approaches in classification of terrorism, indicate, once again, that terrorism is an evolving, multifaceted, and complicated phenomena. The more the political and academic fields gain a comprehensive grasp of that very phenomena, the better they will be to develop more comprehensive typologies. Hence, providing the agencies developing counter-terrorism strategies with an ample perspective to tailor their approaches with a substantial consideration into the similarities and differences of different types of terror organizations. Towards the goals of this particular study, a motivation-based approach is pursued in order to classify terrorism. Motivation-based classification (or segmentation, typology) has been used previously in different fields (see [7] for instance), taking motivation to involve in a certain activity as a basis for classification. In an effort to develop a model of classification for terrorism, taking the motivating factor as a basis seems to be a sound strategy due to the fact that terrorism is, for most of the cases, not an end goal, but a tactic, activity, or means, used in order to realize another broader objective, such as providing a certain ethnic group with more rights, or spreading a religious ideology. Following this very logic with an extensive review of the relevant literature throughout the development of this manuscript, and asking the question of “what is motivating a particular group to rely on terrorist activities?” yielded, a threefold classification of terrorist activities:

1. Ethno-nationalist / Separatist Terrorism
2. Revolutionary Terrorism
3. Religiously-Motivated Terrorism

The following parts of this study examines these types of terrorism in detail including their historical and ideological backgrounds, common tactics, and the examples of terrorist organizations acting with the same motivation.

Ethno-nationalist/separatist (ENS) terrorism has been of great concern since the early 1970s. Among discussions about and fear from religious-based terrorism, ENS terrorism can be considered relatively less concerning for the contemporary world especially after the end or downsizing of violent tendencies of terrorist organizations like Irish Republican Army - IRA and Euzkadita Azkatasuna (Basque Homeland and Freedom – ETA) in Western Europe. With the changing trends in democratic movements and economic developments, ENS terrorist activities also seem to be decreasing in the past years. Europol, for instance, reported that the number of ENS terrorist attacks in the European Union (EU) decreased from 84 in 2013 to 67 in 2014 [8]. It is, however, noteworthy to remind that ENS terrorism is still an important issue for several parts of the world and it is relevant to understanding other types of terrorist activities since many struggles regarding ENS terrorism contributed to the development of contemporary terrorism [9]. In the past three years, for instance, Partiya Karkari Kurdistan (Kurdistan Workers’ Party - PKK), a ENA terrorist group active in Turkey and its southern neighbors, has been in active resistance and fight against a religious-based terrorist organization - Islamic State in Iraq and Levantine (ISIL), which, possibly, is the most concerning of the recent years.

Although it might be traced to much earlier times, the issue of ENS terrorism came to consideration during the 1960s and 1970s with terrorist organizations like Provisional IRA, ETA, and National Organization of Cypriot Fighters – EOKA, and similar others around the world [10]. It, still, is among the major types of terrorism existing around the globe and in the midst of inequalities, tension, hostility and oppression against minority ethnicities and groups in different regions/countries around the world, it does not seem very likely to cease soon. Simply put, the most profound motivation of ENS terrorism is to exculpate the existing ethnic group from the political power and/or to gain political autonomy in the name of an ethnic group [6]. In addition, based on the grievances of the past, they promise to (re)gain economic, political, and cultural rights of that ethnic group as well as opposing to any subordination and cultural assimilation by the dominant national/ethnic groups [7]. While ENS terrorism attempt to forge a national identity, it intends to mobilize a group in the country by utilizing the nationalistic ideologies for a particular ethnic group [9]. Due to this relatively clear and robust motivation for violence, ENS terrorist organizations have been relatively more reachable by the political entities for non-violent settlements and negotiations [11]. In regards to their motivation and longer life term expectancy, compared to religiously-motivated terrorism, it is important to note that these groups base their legitimacy on a collective revolutionary tradition as well. This tradition and its ideological foundation, as will be discussed below, contribute to the life expectancies of ENS terrorist organizations [10].

Since ENS terrorism base its legitimacy on “nationalism,” it is vital to understand what a “nation” is. Although there has been a conventional approach to define “nation” through the mutual cultural features like language or through race and religion, this approach has recently been seriously challenged [6]. Likewise, there is not a consensus on what nationalism is, but it develops itself by definition throughout history which legitimizes its existence for the time being [12]. Amid this vagueness and uncertainty, several approaches to define a nation and nationalism has been widely considered in different disciplines. Benedict Anderson, for instance, is one of the mostly referred scholars in this regard [13]. Anderson considers nation as an imagined community, as both inherently limited and sovereign. His idea of “imagined community” is mostly based on the fact that in contemporary society, members of the nations, even the smaller ones, will never know their fellow members. This approach is relevant to understand ENS terrorism, due to the fact that these organizations want and work towards dictating an imaginary nation (that might not be ethnically and or genetically defined and determined) which is promoted, defended, and fought for by them.

Based on an approach like this and/or similar ones, nationalism is a political doctrine that is more of a concern for understanding ENS terrorism. As a political doctrine, nationalism has three basic claims [14]:

1. There exist a nation with an explicit and peculiar character,
2. The interest and values of that nation have priority compared to others’,
3. The nation must be independent by, at least, the attainment of political sovereignty.

It is also important to note that nation can be interpreted by its civic and cultural facets. While the former one is not based on descent or ethnic origin, but on a common destiny and geographical unity, the latter one relies mostly on blood-linkages as well as language and religious unity [6]. It is hard to interpret that the latter one is leading ethnic nationalism and more prone to be relevant for understanding ENS terrorism. On the contrary, cultural terrorism can, as well, be likely to cause political tension, oppression and inequalities [15]. A good example of that could be given from Turkey, where the official state policy rejected the existence of a nation as “Kurds” in Turkey for about half a century, after the establishment of the Turkish Republic in 1923, which led the establishment and long-lasting destructive terror activities of the PKK.

Nation and nationalism are two important terms leading the discussion to another important term in this context; nation-state. Nation state is a notion developed after the Enlightenment era with the early philosophers’ ideas like Voltaire, Locke, and Montesquieu. They promoted the idea that the best democratic government can be based on a common desire of people to govern themselves as a distinct nation state [16]. This desire to establish and sustain homogeneous nation-states has also been one of the driving forces behind ENS terrorism.

ENS terrorism uses violence in order to make a statement for a particular national identity [16] while it is being used by religious-based terrorist organizations to make a theological statement and by ideological terrorist to make symbolize their ideology. Earlier studies indicated ENS terrorism being the most violent form of terrorism in the modern world [9]. This strategy of relying heavily on violence acts also as a propaganda tool for ENS terrorist organizations. It not only helps ENS terrorist groups convey their nationalistic messages, but also to marginalize the members of an ethnic minority even if they do not bear a strict nationalistic and separatist perspective. This happens through a vicious cycle of violent acts of terrorist organizations, governments’ natural repressive counter actions on these terrorist activities, and the terror organizations’ posing themselves as the victim of an oppressive government led by a certain ethnic group and relying on violence again. The tactical violence employed by ENS terrorism is a strategical follow-up on the tradition of People’s Will (Narodnaya Volya), a revolutionary organization operated in Russia during the late 19th century. People’s Will carried out a terrorist campaign; a new cost-effective struggle against Tsarist tyranny in Russia. They justified the death of innocents as an inevitable consequence of war since they considered terrorism as “an ethically better choice than allowing the carnage that would result from a mass insurrection” [17]. They assassinated Tsar Alexander II, bombed his palace, and attacked other government officials of symbolic significance.

In general, these terrorist organizations, carried out; assassinations of important public figures, kidnapping officials and civilians with symbolic importance, bomb attacks on public places, suicide bombings at government buildings, hunger strikes, hostage taking, and hijacking as their common terrorist tactics. In choosing their targets, ENS terrorist organizations have mostly preferred symbols of political, economic, and nationalist oppression such as banks, ambassadors, and dignitaries. In many cases, these targets have been in and/or around the home country where they fight for the liberation of their nation/ ethnicity. In general, these strategic attacks and activities represent a kind of asymmetrical warfare [18]. For a certain period of time, ENS and ideological terrorism were considered to be the same due to the similarities in their tactics. In the past two decades, however, this approach has been changing and the changing nature of ENS terrorism has been recognized separately [19]. ENS terror has a greater emphasis on nationalism while revolutionary/ideological terrorism is more focused on the rhetoric of revolution and class warfare [20]. In addition, even though ENS terrorist organizations are associated with an ideology, they are not lost in the nihilism of pure absolute goals [9]. ENS terrorist organizations also differ from religious terrorist organization in having distinct and clear goals, such as gaining the liberty of a certain geography or an ethnic group.

Irish Republican Army

The most prominent organization in ENS terrorism is considered to be Irish Republican Army (IRA). Although it has changed over time and evolved to different organizations (like Provisionals and Officials), they are mostly representing a long-lasting Irish nationalist movement reacting to colonial rule of UK. They used terrorist tactics to revolt against British rule. Especially after the establishment of Provisional IRA (PIRA) in 1969, fighting to unite Northern Ireland with the south has been mostly made through a terrorist campaign. This campaign against British army helped IRA unite against British army to increase the number of their supporters. This is one of the examples where violence as a terrorist tactic worked as a great propaganda tool. They employed tactics like bombings, shootings, and hunger strikes [21].

Starting with the early 1990s, IRA and UK entered into a peace process and in 1998 they signed the Belfast Agreement, which entailed the establishment of independent human rights investigations (through Independent Monitoring Commission) and ending the paramilitary organizations. In 2005, IRA officially ended itself and returned its weapons with a call to supporters to cooperate with police.

Basque Nation and Liberty

Another well-known example of ENS terrorist organization is the ETA (Euskadi Ta Askatasuna - Basque Nation and Liberty) which was established in 1959 and remained active until 2011. The goal of ETA was to establish an autonomous country at the northern Spain and Southern France for Basque Nation. The Basque region has its own language and culture but it has not been an independent state for over 1000 years. Starting with early 1940s, with the administration of Franco as the fascist leader of Spain after the civil war, Basque language and culture was oppressed and the region was incorporated into Spain. The major motivating force behind the ETA terrorist movement, therefore, was regaining the liberty of Bask region and its language and culture [22].

At the earlier stages of ETA, violence was not prominent but a stronger emphasis was on national and cultural identity and regional autonomy. Even the earlier acts were not involving violence, but the suppressive counter act by Franco led a vicious and evolving cycle of violence as indicated above during the discussion of how violence can also act as a propaganda tool for ENS terrorist organizations. It was around the 1970s when acts of ETA started to become seriously violent involving assassinations and robbery [9]. While the levels of terrorist violence were escalating to an uncontrollable level, several counter-terrorism groups within Spainish officials were developed and carried out a series of operations without considering the rule of law, torturing and killing several suspected ETA members and supporters. Known also as “death squads,” they assassinated many ETA members, or, sometimes, the people they thought so [23].

The ETA terrorism started to lose its impact and legitimacy in Basque region when democratic developments and rights were granted by the Spanish governments after 1980s. The Basque region was allowed to establish a police force and regulate the local education system as a part of these developments. Regardless of these positive developments and decreasing support, ETA continued its terrorist activities like sporadic bombings until the end of 2010. In 2011, ETA announced that it was abandoning its militaristic activities, but even in 2015 it was indicated that they were responsible for several bombings in touristic areas in Spain. It is, therefore, hard to state that the ETA has totally been eradicated. Yet it is not considered to be as a serious threat as it used to be in the earlier years [9].

The Kurdistan Workers Party

The Kurdistan Workers Party (Partiya Karkerên Kurdistanê - PKK) is an active terrorist organization established in Turkey in 1978. It is acting in the name of Kurds, an ethnic group living in southeastern part of Turkey, northern Iraq, northern Syria and some parts of Iran. The ultimate goal of PKK is to establish an independent Kurdistan as a Marxist-Leninist state. In this sense they also have mutual characteristics with revolutionary terror organizations. They claim a geographical region including some parts of the aforementioned countries where Kurds have been living [24]. Although there was some oppression on the ethnic identity and mother tongue of Kurds for many years after the establishment Turkish Republic in 1923, a considerable development has been achieved in the past two decades in granting major cultural rights to Kurds living in Turkey. These include, but not limited to, the use of Kurdish language in private and public life, publications in Kurdish, assigning original Kurdish names to the Kurdish villages, establishment of university departments regarding Kurdish language and culture.

The region where Kurdish-descent citizens of Turkey have been living for decades, however, has been relatively under-developed in terms of infrastructure and economic production (Foundation for Middle East and Balkan Studies, nd). In addition, Kurdish nationalists have long been striving for other rights such as autonomy of local governments and public education in Kurdish. Like the other ENS terrorsit movements, PKK has also based its legitimacy on these kinds of problems facing Kurdish people mostly in Turkey, but they have extended their claim to other surrounding countries where other Kurdish people have also been living under different state authorities with similar concerns and problems resulted from the policies of oppressive governments. After being established under the leadership of Abdullah Ocalan, a university educated Kurdish nationalist, the Kurdish nationalist movement has become more militarized with well-organized militia forces of PKK, with sometimes more than 50000 active civilian militants since 1978 [24].

The first significant terrorist act of PKK was carried out in 1984 in Sirnak, Turkey. With the support from Syrian government and other possible external sources, PKK has shown to be a major threat for security in Turkey and it has been so for the past 30 years. They have been involved in a series of different kinds of attacks ranging from village massacres to suicide bombings and bombing in touristic areas. The founder and the leader of PKK, Abdullah Ocalan was captured in Kenya in 1999 and he was brought to Turkey where he was adjudicated by the Turkish Court and received a death penalty, which, later on, was converted to a life-time imprisonment upon the abolishment of death penalty in Turkey. The violent acts of PKK had caused about 40000 lives until that time [25]. The violent acts of PKK, however, have not stopped after the imprisonment of its founding leader. It has continued its terrorist attacks in rural and urban areas of Turkey. Recently, starting from mid 2015 to mid-2016, PKK occupied some cities in the southeastern part of Turkey, which causing the death of many civilians as well as PKK militants and security forces.

By the early 2010s, Turkish government started a democratization movement to address the concerns of Kurds. This movement resulted in decreasing violence and diminishing support for PKK. In the meantime, the Kurdish political movement has also gained support by wining local elections in many eastern and southeastern cities of Turkey. By 2013, a series of peace talks started between the representatives of Kurdish political movement and the Turkish government. The positive developments, however, turned around after the June 7th, 2015 elections of Turkey, when the ruling party, Justice and Development lost its majority in the parliament and the Kurdish affiliated party received a record support in its history by winning 80 seats in the Parliament. After this election, the violence escalated to a point where several cities were occupied by PKK and its affiliated forces, and the Turkish security forces responded to that with heavy military operations in urban and rural areas [26].

Similar to the case of ETA in Spain, in Turkey several paramilitaristic government forces were arguably developed and used during the 1990s¹ against increasing PKK violence. This, however, led more violence due to unsolved murders of several Kurdish people, as well as progressive scholars and journalists, which were blamed on to either side of this dispute. Another important feature of PKK has been its active role in drug smuggling and other organized smuggling activities in the region. It is estimated that PKK gains about 2 Million dollars from marijuana production and trade, and 1.5 billion dollars in total from overall drug smuggling [27]². In this sense, it is similar to several other terror organizations such as The Revolutionary Armed Forces of Colombia (FARC) and Liberation Tigers of Tamil Eelam, which also relied heavily on drug trade for financing their terror activities. As of mid-2016, PKK has been an active ENS terrorist organization mostly operating in Turkey very violently in the midst of ongoing and escalating turmoil in the region, it does not seem that it will end very soon.

It is extremely challenging to develop and utilize the most appropriate terminology in this kind of terrorism, where a phenomena which exists on the earth to bring peace to human beings is combining with one of the most horrifying phenomena. There is an ongoing discussion, on defining and naming the type of terrorism that occurs in conjunction with religious motivations, and conventional and endemic violent tactics of terror carried out by different actors around the world in a systematic and organized way. Some scholars, like Tucker et al. [28], even argue against the use of terms “religious terrorism. Within the scope of this chapter, the term “religiously-motivated terrorism” is preferred to classify this type of terrorism, but Ranstrop et al. [29] term “terrorism in the name of religion” is also a perfect reflection of what this type of terrorism is and how it can be classified, as well. According to Ranstrop, religiously motivated terrorism “has become one of the most vibrant, dangerous and pervasive trends in the post-Cold war world.” Religiously-motivated terrorism (RMT), in addition, seems to be the most recognized and concerning type of terrorism especially in the western countries like the US and many other European countries during the post-9/11 attacks event.

Amid this terminological and conceptual complexities and discussions, it is hard to come up with a precise definition for RMT. The definition by Gregg et al. [30], neverthelss, is comprehensive in coverage and up-to-date representing the recent trends in RMT. Gregg defined RMT as “the threat or use of force with the purpose of influencing or coercing governments and/or populations towards saliently religious goals” (p.39). RMT is mostly regarded as being affiliated with Middle-east and Islam. It, however, has a broader coverage and longer history than Islam and the terrorist activities in the name of Islam. Different religions have been used as a basis and legitimizing ground for several fanatic and violent behaviors. An example of that includes the Jewish fundamentalist Kach movement which, motivated an attack on praying Muslims in West Bank, causing 29 deaths in 1994. Likewise, the Japanese religious cult Aum Shinrikyo can be another example which was responsible for notorious sarin nerve gas attack in Tokyo metro in 1995. Lastly, religiously-motivated bombing of US Federal Building in Oklahoma City by two white Americans can be another example where terrorism was carried out in the name of a religion.

Hoffman [10] indicates that there has been an increasing trend in the RMT activities since 1968. Between 1960s and 1990s, the number of different RMT groups almost tripled. It has become more preeminent and concerning especially during the post Cold Was era as the result of increasing ethnic and religious conflicts in the different regions of the world. Ranstrop [29], indicated this trend as follows:
“The accelerated dissolution of traditional links of social and cultural cohesion within and between societies with the current globalization process, combined with the historical legacy and current conditions of political repression and economical inequality and social upheaval common among disparate religious extremist movements, have all led to an increased sense of fragility, instability and unpredictability for the present and the future.”

Even though they are affiliated with different religions, all of the RMT activities carried out in the name of religion share one mutual characteristic; they all believe that their acts are a reflection of obeying God’s (or a kind of supreme power’s) orders. It is a sacramental act and divine duty that needs to be carried out as a response to a theological requirement. This understanding brings a limitless area for RMT acts where there are no restrictions resulting from political, moral, and/or practical considerations [31]. Unlike other terrorist organizations, RMT is primarily motivated by religion, but they may also develop several other secondary concerns and justify some of their acts through these motivating forces, such as political considerations of a specific term or a region. In some instances, this complexity makes it difficult to distinguish political and religious aspects of RMT. Activities of Hamas in Palestine, Hizb’Allah in Lebanon, and Turkish Hizb’Allah in Turkey can be identified as examples of this complexity [29]. Likewise, Bin Laden was motivated to eradicate the heretical royal family in Saudi Arabia and motivated his militia to assassinate Prince (now King) Abdullah of Jordan [9]. It is, nevertheless, considered to be important to distinguish religiously-defined motivations (apocalyptic, millennial, and/or messianic) of these groups from politically-defined motivations in order to develop effective counter-terrorism strategies [30]. This complexity of religious and political objectives actually indicates also the very fact that RMT has actually resulted from a perception of crisis in a group’s social, political, economic, cultural, and spiritual environments. RMT can be observed as a reaction to this crisis milieu through which a fight for existence and survival justifies a legitimate reaction and defense to several perceived threats and uncertainties in this environment [29,32].

Amid this complexity and interwoven motivational structure, the objectives of RMT can also be defined as either immediate or ultimate objectives. In this sense, the former one, immediate objectives, are usually related to the political motivations of these organizations to establish a religious government. The latter one, on the other hand, is mostly apocalyptic and/or messianic like conveying God’s message to everybody [33]. In addition to this dual taxonomy, Gregg [30] indicates apocalyptic goals as another important motivation for RMT. The apocalyptic motivation, in his sense, refers to causing “cataclysmic destruction to people, property, and the environment with the hope of fomenting the end of time and ushering in religious promises of a new world (p.39). Gush Emunim, in Israel, is an example of RMT organization mostly bearing an apocalyptic motivation. They are involved in acts to create needed catastrophic conditions to hasten the coming of the messiah [31]. Another example, from the US, would be The People’s Temple, which led to the group suicide of 900 people. The last group, although standing as an example for apocalyptic motivation, may not qualify as a terrorist organizations. Japanese group Aum Shinrikyo, on the other hand, can be another example of RMT groups acting on these motivational grounds [30].

Creation of a religious government, on the other hand, is another important motivation for RMT. This is mostly the case for jihadist Islamic militants where they strive to establish an independent state governed by Islamic Law (Shari’a). ISIL, for instance, claim to be a state governed by Islamic law and the leader of this group calls himself Calipha. In this sense, Al Qaeda, which preceded ISIL, also intended the creation of Islamic Caliphate beyond the borders, as a super-state. This is, however, not endemic to the Islamic groups, but there are examples from other RMT organizations as well. Timothy McVeigh, the Oklahoma bomber, for instance, was connected to Christian Identity Movement and Covenant, and the Sword and the Arm of the Lord (CSA). These groups were also intending to establish a Christian state within the US [30]. Lastly, religious cleansing is another important motivation for RMT groups. Based on this motivation, they intend to eradicate infidels from their religion, either within or from outside of their religion. This is mostly based on how they interpret a certain religion or religious script and teaching, and how others differ from them in their understandings and practices [30]. Turkish Hizb’Allah, for instance, assassinated several “infidels” in Turkey and buried them in cement. Likewise, ISIL has been carrying out terrorist attacks in Muslim countries, including Turkey and Iraq with this motivation. Yitzhak Rabin’s assassination in Israeli by a Jewish fundamentalist was another example of RMT acting because of this this motivation. This motivation of RMT is similar to ENS terrorism’s ethnic cleansing objective, but driven by religious considerations and within the same religion.

RMT tactics are similar to the tactics of ENS terrorism, relying heavily on violence. RMT has also some distinct tactical features. Targeting governments and the higher officials of the existing governments has been one of the important tactics especially when they are acting with the motivation of establishing a religious governments. Assassinations of Israel’s Prime Minister Rabin and the Egyptian President Sadat are two prominent examples of this tactic. If they are motivated with causing the end of the world, they rely heavily of catastrophic events that would cause major losses. The Tokyo Metro sarin gas attack and Oklahoma bombings are the examples of this tactic [30]. Several types of attacks of different magnitudes on a religious enemy have also been another common tactic employed by RMT. The 9/11 attacks in the US by Al Qaeda is the most prominent example of this tactic. The latest bombings in European cities (i.e., Brussels, Paris, Istanbul) by ISIL as well as the Jewish terrorist organizations’ attacks on Palestinian people or Hezbollah’s attacks on Israeli cities are among the commonly known examples of this tactic; the most important goal is to harm and destroy the enemy. Several other targets in these attacks may also be purposefully chosen, as well, to convey a message, or to cause a specific type of harm. In 9/11 attacks, the Pentagon was targeted as the representative of military forces, the Twin Towers represented the capital power of the western world. Similarly, in one of the recent attacks in 2016, Istanbul’s major international airport, of great importance in Turkey’s economical life, was targeted which is. Previously, another attack on Kurdish protesters in a Turkish city in 2015 was a similar tactic against the “enemy” groups.

Although bombings seem to be the most common type of attacks carried out by RMT, suicide bombings can be considered as the most distinct.. Since the overall religious motivation of RMT claims that they are carrying out the wishes of their God in whatever they are doing in their ideology, dying on this way is also considered a holy and invaluable self-sacrifice. Martyrdom is the ultimate goal, for instance, for Islamic militants who commit suicide bombings. In this type of attack, the attackers, suicide bombers, have no concern for getting caught. Developing counter strategies for suicide bombers, therefore, has especially been challenging..

As mentioned before, especially in the contemporary discussion of terrorism, RMT is the most concerning terrorism type and most of the terrorist organizations in this group somehow relate themselves to Islam as a religion. However, RMT does not only consist of terrorist organizations defining themselves through Islam; there are several other RMT organizations affiliated with other religions. Since most of the existing studies cover RMT organizations rooted in Muslim geographies and defining themselves through Islam and these types of terrorist organizations, two non-Muslim RMT organizations are included in this study: Kach Movement and Aum Shinrikyo.

Kach Movement

Kach movement was started as a political party in Israel in 1971 by Orthodox Jewish Rabbi Meir Kahane. This movement is also referred as Kahanism or as part of a split group known as Khanne Chai. Kach is a militant group mostly motivated with the objective to banish Arabs from holy Israel lands and to establish a pure Jewish state. It has been listed as a terrorist organization by the US Department of State since 1994 [34]. Kahane was born in 1932 and educated in the US as a lawyer and rabbi. He was influenced by Revisionist Zionist movement’s ideology, which aimed to establish a Jewish state in all of British-ruled Palestine. In 1968 he established the Jewish Defense League (JDL), which urged Jewish Americans arm themselves to combat against anti-Semitism. They targeted Soviet-block nations, the Palestine Liberation Organization, Arab states, and several Jewish organizations that were considered moderate [35]. Kach was an outpost of this early movement and its original teachings. JDL and Kach, therefore, may be cited together as a terrorist organization [30]. JDL carried out about 15 terrorist attacks in the US between 1980 and 1985 according to the FBI statistics [36]. Kach advocated that the Halakhah, the Jewish religious law, should govern the state of Israel. It also advocated an anti-Arab policy in Israel for a long time and condoned violence as a legitimate strategy to reach the aim of establishing a religious and homogeneous (all Jewish) state [37]. Until 1984, Kach was banned from entering the elections in Israel due its racist and extremist propaganda, but he won the elections at that year. Kahane was assassinated in 1990 and another group Kahane Chai split from the main party. Both movements remained active following the same ideology until the end of 1993. In that year, they were banned by the Israeli government. The ideology of Kach, however, remained active as a movement even after the political part was disbanded [35]. One of the most important attacks that Kach supported was an attack on worshipping Muslims in Al-Ibrahimi mosque in West Bank. It engaged in several activities, using explosives and firearms to cause substantial damage (i.e., a car bomb attack), threating, conspiring to carry out assassinations, and soliciting funds and members for terrorist activities.

Aum Shinrikyo

This Japanese-oriented terror organization is also known as Aum and Aleph which means (the “supreme truth,”) but it is usually referred as Aum. It was established by Shoko Asahara (or Chizuo Matsumoto, his real name) and gained religious organization status in Japan in 1989. The group has been representing ideas and teachings from Hinduism and Buddhism, but it also has incorporated several elements from Christian apocalyptic teachings. Asahara represented himself as Christ, and the “first enlightened one” since Buddha. He preached the idea that the end of the world would come in 2003 upon the US’s initiation of the WW3 with Japan, and his followers would be the only ones to be saved [38]. The group was a designated as a terror organization in both US and Japan [39]. Starting its activities during the 1980s, the group gained a significant amount of supporters especially among young university students, through the speeches at universities and the books that Asahara published. At the time of the 1995 attacks, it reached about 40,000 followers. The teachings of Asahara promised these young people a relief from the contemporary pressures resulting from academic and professional life. Later, participants indicated that the group activities and camps that they attended were kind of “mind control… sort of like magic.” The father of a young cult member stated that “Aum turned our children into mindless people without a sense of their own free will” [40]. The original group was dismantled in 2000, but two offshoot groups, Aleph and Hikari were established after 2000. Today, these groups are believed to have about 1700 members mostly in Japan, but also in Russia and several other European countries. These two groups are still under the close scrutiny of Japanese authorities [40].

The group involved in several violent acts including killings, kidnappings, and using biological and chemical agents. One group leader, Nagaoka, who opposed Asahara’s cult, for instance, was attacked with VX verve gas right before the group’s infamous attack on the Tokyo metro, which took place on March 20th, 1995. During rush hour, the group brought a liquid into the train cars of the Tokyo metro and punctured the bags with umbrellas releasing the gas into the train cars. This attack created a shock effect in Japan, which was known with social cohesion and low crime rates. The attack killed 13 people and injured about 6,000 others creating a long-term effect in their lives. Between 1995 and 1998, the group attempted several similar attacks, but could not complete them successfully. Thirteen members of Aum, including Asahara, were sentenced to death after the trial [38,41]. After the attacks, it was discovered that the group was originally planning greater massacres by spraying botulin, a kind of legally accessible biological toxin, from buildings and converted delivery vans. This plan, however, did not work and the group started to experiment to produce chemical gases through the studies and experiments of young scientist members of the group. Conclusively, they were capable of producing thousands of kilograms of sarin gas. At one point they even acquired a Russian helicopter to use during these projected attacks. It was, later during the investigation of the metro attack, discovered that the group previously released Anthrax spores, collected Ebola virus samples from Zaire, and released sarin gas in 1994 in a neighborhood killing seven and injuring about 1,000 people [42]. The activities of the group, however, have not stopped. The two offshoot groups were found to be active in Russia, Europe, and Slovakian countries in 2015 and 2016 [39].

A difficult term to define, “revolution,” refers to a series of actions and strategies leading to a major change in the society. The term ‘revolution” has also been used to describe radical and transformative changes in different fields or phenomena, such as industrial revolution. This change can be achieved through a group of diverse strategies and acts, and a revolution can represent uniqueness from birth to end [43]. Starting from the American Revolution and followed by French, Soviet, Turkish, Indian and Iranian revolutions, the world has witnessed this transformative and dramatic change in political arena leading to liberation, democratization, modernization, regime shift, and ending the existing political systems in many countries around the world in the past three centuries. The latest Arab Spring movement also caused some type of revolution for the countries like Tunisia and Egypt in North Africa in the last century, while the political turmoil and instability is yet not finished.

Revolutionary terrorism (RT) usually refers to terrorism being used as a tactic by the reformist or revolutionary organizations who would like to achieve this transformative and dramatic change in the political structure or existence of a government [44]. Pumphrey et al. [45] indicated that these reformists are mostly intellectuals and they “revert to tactics of spectacular violence, in the hopes of extorting concessions from the ruling elite in order to take a "shortcut to revolution." They labor under the illusion that the ruling circles can be ‘terrorized’ into giving up power or, at least, making meaningful concessions to the movement of the ‘powerless.’” Taylor et al. [46] also used the term ‘political terrorism” referring almost to the same phenommena meaning “a symbolic act designed to influence political behavior based on extranormal means, entailing the use or threat of violence.” Hutchinson et al. [44] indicated that “revolutionary terrorism is a part of insurgent strategy in the context of internal warfare or revolution: The attempt to seize political power from the established regime of a state, if successful, causing fundamental political and social change.” She also indicated that these revolutionists do not rely only on violence as their unique instrument to reach their end goals, but it usually is a major one for them.

At this point, it is vital to distinguish a revolutionary warfare from RT. The American Revolution, for instance, was not a RT, due to the fact that the violence was against the British army, not against any British citizen to create fear. Likewise, no symbolic targets were selected and destroyed to cause horror, through which the change of political behavior of British power would be sought after. Indeed, the US army, at the beginning, mostly consisted of guerillas, but most of them joined the Army lines and involved in regular warfare, not terrorist attacks [9]. It is important to note that fighting for a change through conventional warfare is significantly challenging and tough. It also requires a systematic approach, preparation, and solid financial support. Although relying on terrorism, on the other hand, is relatively easier, simpler, and achievable, it might not be effective in reaching the end goals. RT can be carried out through a group of militia, not soldiers, who may not be trained in the rules and tactics of warfare and can use alternative weapons, even a knife or amateur bombs. These people are not required to wear uniforms and they can even keep their civilian lives active and productive to maintain themselves and even to contribute the organization’s finance [44].

RT has roots embedded in the political theory and ideological grievance. Political ideology refers to “the set of beliefs about the proper order of society and how it can be achieved” at an individual level [38]. In this sense, RT is referred to as utilizing terrorism as a part of a revolutionary process to change political ideology at both individual and societal levels [46]. RT started mostly after WW2, involving mainly leftist and Marxist political ideologies. Later on, rightist groups have also followed the tactics of these earlier RT groups [9]. The terms “leftist” and “rightist” actually were rooted in the French governmental system, starting from the French Revolution, where the ‘leftists” (or left of center, leftism, left-wing politics) were considered as both liberal and anarchist radical politicians while “rightists” were involving more conservative politicians. Leftists, in this dichotomy, were in support of revolution in order to dismantle the monarchy and create a secular republic in France. Rightists, on the other hand, were in favor of protecting the existing institutions and systems of the former regime [41]. Leftism supports the idea that, simply put, human development will illuminate if individuals can cooperate with each other through respectful relations, which can be achieved when disproportionate differences in status, power and wealth are eradicated [47].

Generally, the leftist perspective is mostly based on the theoretical frameworks developed by Karl Marx and Friedrich Engels during the early 19th century. Marxism is an ideology that intends to change the existing capitalist structure to bring better life conditions and further rights to the working class who, in this perspective, are believed to be corrupted and oppressed by the capital holders / upper class. The question, then, becomes on making that provisioned change. Marxism is mostly discussing overthrowing the government as opposed to maintaining law and order - revolution and anarchy verses peaceful change. These perspective mostly affected revolutionary movements all around Europe during the second half of the 19th century, but most of them were not able to carry out their revolutionary intentions. Yet, these movements and the violence utilized during this term created a long-lasting impact on the forthcoming revolutionary movements all around the world [46].

In the Marxist ideology, capitalism was considered as a means to exploit people and their labor as well as pitting them against each other because of the free market, competition, and private ownership of property. Marx argued that his theory was based on ending this class struggle by ending the properties of capitalism and establishing communism. Communism is characterized by totally eradicating private ownership and governments while socialism is a transitionary period towards this utopia. This overall Marxist perspective would be converted to violent revolutionary movements through a revolutionary vanguard. A vanguard is a group of working class revolutionist who initiate and organize the revolution and expand it to other people in the society, and abolish the ruling class’s power. Lenin, for instance, considered his movement towards revolution as the vanguard [48]. Taylor et al. [46] indicated that;“the vanguard exploits the differences in people existing in a heterogeneous population. They use differences among people to agitate and disrupt society, while at the same time attacking government through a variety of tactics. Terrorism is perceived as a legitimate military tactic designed to show the weaknesses and vulnerability of the existing government. As the government “cracks down” on individual civil liberties in an effort to stop terrorism, mass society further fractures with open antagonisms between groups of people and disruption of the existing way of life. Social order decays into rioting and eventual revolution.”

Anarchism is another important perspective in left-wing political ideology. Basically, anarchism promotes a self-governed society based on voluntary intuitions as well as voluntary cooperation and association between individuals, also referred as “non-hierarchical free associations.” This anarchist perspective advocates a stateless society, considering the state as potentially harmful and unnecessary/undesirable due to human beings’ capacity to establish and maintain non-hierarchical free associations [45]. In that sense, anarchism intents to eradicate classical hierarchical, central authorities as well as government structures and institutions based on, again, a classist, hierarchical structure. Instead of this system, they fought for the people of middle and working classes to be the owners of all property and totally abolish governments (stateless society utopia) [46]. The anarchist perspective has evolved into different versions and wings over the years, such as social anarchism, collective anarchism, and anarcho-communism. This diversity makes defining and understanding anarchist terrorism a challenge as well. Followers of Blonqui, for instance, are supporting the idea of being organized as combat-ready small groups and key officials, organizations and institutions because they are suspicious of both the government and the society on their way to revolution [49].

Widespread use of violence in leftist political ideology started primarily following the writings of Necheyev and Bakunin. They promoted violence as principal means for revolution. In using violence, people supporting revolution were to infiltrate into the social groups to gain their support and organize themselves into small combatting groups to attack against the enemy, according to Necheyev and his followers. These perspectives led the use of explosives and mass killings as well as political assassinations, all of which have been followed by the contemporary terrorist organizations as well [46].

Hutchinson (42) indicated that the RT have some essential properties including;

1. Use of terror as a part of revolutionary process to seize power from an existing government,
2. Manifestation of terror in unacceptable violent acts,
3. Being selective and representative for the victims and targets in its acts,
4. Intending to create fear and confusion on specific groups to change opposing political behavior and attitudes.

Use of violence is actually a must as a tactic for RT organizations, not a choice against non-violent propaganda for change and reform. This is both a conceptual shift from political revolutionists as well as the representation of a fact that the non-violent alternatives may have had existed even before the RT activities started and could not achieve to create the anticipated change. RT activities usually involves monstrous violence towards or within a civilian population. By employing violence as a tactic, RT intents to create extreme fear just as any other type of terror; symbolically designed to have a devastating impact on the existing government [9]. Through this fear, they intent to suppress any opposition to the revolution, not to convince people to support them. Another important outcome of RT activities is the polarization of the society through coercively influencing the behavior and the attitudes of people in the society [44]. Although RT initiates actions to carry out a revolution, it may soon return to focus on its own survival. After considered outlaw by the existing government, and lacking a strong support from the society, they usually covert their activities and start to maintain their existence more than fighting for a chance. The RT activities, thus, tend to convert to be personal rather than political after a series of initial violent attacks [50].

In the historical development of RT, Tupamaros, officially known as National Liberation Movement, played a great role. Established in Uruguay during the early 1960s, Tupamaros targeted a revolution in Uruguay to end the repression over sugar workers and to end all other economic and social problems existed in the country after 1950s. From an historical perspective, it is important to note that Tupamaros was the first RT group that brought violence into the urban areas. Earlier examples of revolutionist movement, like the Cuban movement, were mostly involving guerilla fights in rural areas. In addition, instead of building a regular army force, they slowly gathered sympathizers, arms, and finance to support their urban guerilla attacks. Using a decentralized structure, they carried out wide-spread violent attacks in different parts of the country. Tupamaros is an important group in the historical development of RT because their organization’s strategy (decentralized cells at the bottom and national convention at the top), division of labor (militant and logistic units), and urban-based terrorist attacks with tactics like bank robberies and kidnapping people with political and diplomatic importance, set an effective example for other revolutionary terrorist organizations in the western world [9].

Red Brigades

In Europe, during the rise of New Left movement starting from the early 1960s, several groups embracing extreme leftist ideas emerged, mostly in form of human rights advocacy. They strongly opposed the capitalist Western powers and identified the citizens of underdeveloped world as the new working class of the world. They mostly fought to overcome this global class struggle [46]. Italy was one of the European countries which experienced a series of failures of moderate leftist governments during the 1960s and 1970s. These failures in economic and social arenas led massive protests by workers and student groups. Amid these social unrest, several extreme leftist groups emerged and started to advocate for class warfare, and to utilize violent means. They were advocating the idea that the Italian Communist Party and other representatives of the working class lost their original focus and distanced from the basic ideology of communism. Red Brigades (Brigata Rosa) was one of these groups that would develop and became very influential as a RT organization in Italy [51].

Red Brigades was one the most influential Europe-based RT organizations established in 1970 in Italy and remaining active for about 20 years, it was involved in more than 14,000 terror attacks including the killing of Aldo Moro, former prime minister of Italy. Red Brigades aimed to create a revolutionary state through armed struggle, following the food steps of Tupamaros, utilizing urban guerrilla warfare as a major tactic. In this respect, they conducted kidnappings, murders, factory sabotages, arsons, and bank robberies. In these attacks they targeted factory owners, the leaders of right-wing organizations, magistrates, politicians, and public officials. They declared the Christian Democratic Party of Italy their major enemy [52]. During the 1980s, Italian security forces carried out effective operations against Red Brigades, resulting a significant number of arrests at the leadership level. Those arrested members of the group cooperated with the law enforcement and helped them reach other members as well. In 1981, the group was split and mostly ended its violent activities. Among the offshoots of the group, Red Brigades Fighting Communist Party (BR-PCC) continued attacks even during the 1980s. It declared an end for their armed fight in 1988 [53].

Revolutionary People’s Liberation Party/Front

Revolutionary People's Liberation Party/Front (Devrimci Halk Kurutulusu Partisi – Cephesi – DHKP-C) is a RT organization based in Turkey. It was formally named DHKP-C in 1994, but it is a fraction of a revolutionary leftist movement going back to 1970s in Turkey. It is considered a terrorist organization by Turkey, EU, and US. Similar to the trends in other European countries, Turkey also experienced leftist movements during 1960s and 1970s. The earliest organization leading to DHKP-C can be identified as THKP-C (Turkiye Halk Kurtulusu Partici – Cephesi) which was established in Turkey in 1970. THKP-C was a movement rooted in Turkish Workers Party but it opposed and criticized the party and other leftists of that time for being reluctant and passive in their revolutionist activism. The ideological philosophy of THKP was developed by Mahir Cayan. In this ideology, he promoted the thesis that Turkey was covertly invaded by international imperial forces starting in the 1950s. He also declared that their movement was a part of international revolutionary movement. US and other western countries, thus, considered as major enemies of the group in addition to Turkish regime. In addition, they were also considering the Middle-East as oppressed by imperial forces and in need of liberation. The earlies act of the group was kidnapping, and later killing, Efraim Elrom, the Israel embassy of that time. In the following years, Turkish law enforcement officials captured several members of the group and they were sentenced to death by the court who involved in this murder. In 1972, they kidnapped three NATO soldiers (two UK and one Canada citizens) from a NATO base in Turkey. During the operation to save NATO soldiers, Turkish forces killed nine militants, but the kidnapped soldiers were killed too by the militants. In the same year, the group also hijacked an airplane [54]. The group, however, spitted into smaller groups and ended due to massive arrests and deaths of the leaders in the group.

After THKP-C, two other groups were among the precursors of DHKP-C; Revolutionary Way (DEV-YOL), which remained active between 1974 and 1980 and Revolutionary Left (DEV-SOL) established in 1978 and converted to DHKP-C in 1994. Both of these groups, regardless of several ideological conflicts and counter arguments, mostly followed the THKP-C’s revolutionary leftist tradition. They were involved in numerous significant terrorist activities in those years. DHKP-C was established by Dursun Karatas in 1994 upon the decision of DEV-SOL to establish a party. The primary purpose of the group was to abolish the existing Turkish regime and establish a Marxist-Leninist government. They have adopted the urban guerrilla strategy and carried out several terrorist acts in accordance with that strategy. They are organized through urban cells at the bottom and a commission at the top. The group became well-know when they murdered Ozdemir Sabanci, one of the owners of the largest company, Sabanci Holdings, in Turkey in 1996. The members of the group were trained in several camps based in Greece, Lebanon, and Syria. The group attacked other symbolic targets, like large companies, law enforcement officers, and party buildings. They were also responsible for killing drug dealers in a part of Istanbul, where the group was active in recruiting members and carrying out propaganda activities. Another significant tactic employed by the group was hunger strikes in prisons.

The last important attack of the group was against a public prosecutor, who was prosecuting the killing of a child, Berkin Elvan, by police during the civil unrest in 2013 in Istanbul. The two members of the group killed the prosecutor Mehmet Kiraz in his room in the court building with firearms. The two militants, who carried out that infamous attack were killed during the police raid right after the case in the very same room. The founder of the group, Dursun Karatas, died in 2008 but the group is still active and the three leaders of the group, Musa Aşoğlu, Zerrin Sarı ve Seher Demir Şen are sought by Turkish and US governments. The US Department of State's Rewards for Justice Program is offering $ 3 Million for information leading the location of these three DHKP-C members.

Defining terrorism has long been an issue for both academicians and practitioners dealing with it. One of the important outcomes of that ongoing struggle to is to declare a “problem in problem definition” [4] when it comes to the terrorism phenomena. An extension of this problem is on classifying terrorist activities. As indicated above, making an effective classification is expected to contribute to a through scientific study of terrorism, and a well-informed and specialized counter-terrorism strategies for different types of terrorism, and terrorist organizations, alike. One of the most important outcome of this extensive review is to demonstrate that motivation of a terrorist organization would create a change in the overall activities as well as tactics and targets of their terrorist activities. As a result, first, academic studies on terrorism should develop varying theoretical approaches in examining these organizations. Second, anti-terrorism policies and strategies should consider the differences of these terrorist organizations, following the model offered in this study, in order to increase the effectiveness and efficiency on preventing terrorism and reduce the harm caused by terrorist attacks.

On the other hand, this review indicates, regardless of the motivational differences, terrorist organizations have also similarities, especially in their tactics. Since the overall objective of terrorism is to cause frustration and fear on larger populations, tactics like bombing, or assassinations might be mutually used. The operationalization of these tactics, nevertheless, varies across the different types of terrorist organizations. Killing of individuals who are of symbolic importance for the motivational basis of a terrorist organization, for instance, is a common tactic in different terrorist organizations. Recently, yet, ISIL used beheading as a distinct operationalization of this very tactic. The discussion of the reasons to use beheading is beyond the scope of this review study; however, focusing on the motivational foundations of this terrorist organization can shed light on this discussion. This study, in addition, reveals important challenges in understanding terrorism and terrorist organizations through a motivation-based model of classification. This challenge is regarding the use of certain terror organizations as a proxy for other types of organized criminal activities, espionage operations, or personal criminal activities. For instance, several terrorist organizations, regardless of their motivational-basis, involved in activities like drug trafficking. Likewise, they are thought to be used to as hitmen for different parties. This challenge hinders the capacity of a motivation-based model of classification in understanding some terror organizations [55-57].

Another important challenge, revealed through this study, is the internalization of terrorism. While international terrorism is referred as a type of terrorism in some sources, understanding the “internationalization” of terrorism as a trend, seems to be more noteworthy. Regardless of the motivational basis of terrorist organizations, as examined in the model proposed in this study, most of the terrorism activities has been carried out in a borderless, sort of a transnational manner. The terrorist organizations have ties with other countries, people sympathizing with their motivational basis live in other countries and support them, and they carry out attacks on the soil of other countries. The examples can be increased; nonetheless, most of the contemporary terrorist activities and organizations cannot be examined on a single geographical location, or on a single cultural background per se. In this sense, the proposed model of classification, should be used in understanding the fact that motivational-basis of a terrorist organization is intermingled with its international connections and the dynamics resulting from that internationalization trend.