Civil wars have been studied from various angles, discussing why they occur, when they are particularly violent and when they end. To this end, group interests and inequalities in economic, political or social dimensions have been analysed. However, research has often overlooked a central defining component of rebel organisations, and therefore civil war: ideology. This is partly due to difficulties in observing and operationalising ideology. Nevertheless, all rebel groups have one by which they frame their cause, and which may determine their organisational structure, as well as patterns of recruitment and violence. Arguably, not all rebel organisations are extremist, although they violently oppose a government. Looking at recent wars, extremism—especially religious extremism—seems to increase. The entailing question, in which contexts wars are justified with (extremist) religious ideologies, has not yet been answered satisfyingly. What is being neglected in existing attempts is a social-psychological view: while psychological explanations of radicalisation are manifold, they are rarely being considered as explanations for group- and national-level developments. Therefore, modeling data on religious ideologies in conflict (RELAC), I argue that while significance loss increases the likelihood of any type of rebel organisation grouping, societies with recent experiences of mortality salience are particularly receptive to extremist religious ideologies.