There is some debate in the literature as to what the word ‘extreme’ means because determining what is extreme is a subjective exercise. For the purposes of this review, extremism is the rejection of other perspectives, when one’s own views are thought to be exclusive (Davies, 2009). However, it does not simply “refer to a rejection of liberal values” or anti-democratic views (Kundnani, 2015, p. 26). Nevertheless, there are two attributes that are important when talking about extremism: (1) the political beliefs of extremists are not widely shared even within their own societies; and (2) extremists lack the means or power to obtain their goals on their own. Both traits are important in understanding their choice of strategy (Lake, 2002, p. 18). That is why extremist violence is used as a “form of communication that interacts with other forms of social and political communication” (Crelinsten, 2010, p. 77). Violent extremism there- fore is defined “as those activities and beliefs which are used to advocate, engage in, prepare, or otherwise support ideologically-motivated violence to further socioeconomic and political objectives” (Mirahmadi et al., 2015, p. 2). This leads to radicalisation when it forms a moral hierarchy, in which extreme positions are justified on moral grounds.