In terms of targeting, many of the tactical means and methods of modern terrorism have, until relatively recently, followed those utilized between States in their armed conflicts inter se. It has been argued specifically that, a century ago, terrorist codes on targeting victims closely resembled professional military codes, in that they respected the distinction between soldiers and officials on the one hand, and innocent civilians on the other (e.g., the targeted assassination of Archduke Franz Ferdinand of Austria on 28 June 1914) (Walzer, 1977, pp. 197-234). This was the case from approximately the mid-nineteenth century onwards, when increasingly industrialized weaponry facilitated a lack of targeting, in the sense that killing the enemy became more indiscriminate and deadly. The industrialized and indiscriminate means and methods of warfare utilized during the two "total wars" of the twentieth century (e.g., in widespread disregard of the principle of distinction) effectively taught those who would become post-war revolutionary terrorists, and who also would adopt more irregular weapons and forms of fighting, such as urban guerrilla warfare. In the contemporary world, indiscriminate weaponry (e.g., high-level bombing capacities, weapons of mass destruction (WMDs), and so on) is a recurring feature.
In terms of terrorist strategy, a useful way to conceptualize the evolution of modern terrorism as a resort to revolutionary violence is provided by David Rapoport's influential concept of the "waves" of terrorism ( 'The Four Waves of Terrorism'). For example, one wave is the late nineteenth century/early twentieth century "anarchist wave". Another is the "anti-colonial wave" (starting with the post-World War I political principle of self-determination, e.g., the Aaland Islands arbitration in 1921, and its violent evolution into a legal right after World War II, examples being the Algerian Civil War and the Vietnam War).
In turn, the tactics employed in each of these waves often mirrored those utilized between States during armed conflict, not least because demobilized soldiers throughout the ages have returned to their homes at the end of a war fully trained tactically to utilize force, while the name of each terrorist wave reflects its dominant strategic goals. The wave theory further reflects that terrorist groups rise and fall, that they can dissolve when no longer capable of inspiring others to continue with violent resistance to authority, to violently redress one or other grievance, or to protest violently against a lack of political concessions. This point also suggests that terrorism and its motivations are clearly impacted by the conditions of and changes in social and political cultures.
In contrast, Parker and Sitter (2016) posit that violent terrorist situations occur around the world not so much in waves, but because terrorist actors are motivated differentially through four goal-oriented strains: socialism, nationalism, religious extremism or exclusionism. These underlying motivators are not chronologically sequential, i.e., one strain dies and a new one arises. Instead, they can work in parallel, and can occasionally overlap, to motivate different terrorist movements according to their needs.
Such academic discourse offers a flavour of some of the discussions and debates that occur when seeking to better comprehend or categorize "terrorist" groups. This University Module Series, however, does not take a view regarding what the motivational factors of various non-State actors may or may not be. These are issues that those teaching this or any other parts of this University Module Series may wish to explore further within different contexts.