This chapter turns to the first of the three macro-political events whose conjunction – against the unusual baseline described in the previous chapter – led to the genocide: Rwanda’s civil war or 'security'. It explains how, as the security threat intensified, it helped push party politics to fracture at the elite level into extremist and moderate factions. It also shows how the war affected ordinary Rwandans below. It identifies four psycho-social mechanisms through which war-time threat radicalized those parts of the general population directly exposed to the insecurity. Boundary activation, outgroup homogenization, ingroup unification, and legitimation of outgroup targeting all increased as the threat intensified. At the same time, the chapter also shows that most Rwandans were not radicalized before the genocide began. It suggests, instead, that some radicalized as a consequence of participating in the violence. The chapter also argues that the importance of Rwanda’s civil war should not be overstated. While many genocides have occurred during civil wars, most civil wars have not led to genocides. Rwanda’s civil war was a necessary but insufficient condition for the genocide.