This chapter takes the Chetniks as its case study to argue that the Yugoslav Civil War that accompanied the Second World War is best understood when accounting for mass violence and collaboration. The civil war against the Partisans and the Chetniks’ collaboration with the Axis helped facilitate the mass violence perpetrated against outgroup populations, namely Bosnian Muslims, ethnic Croats, and communists, both real and perceived. This chapter begins with the resistance to the Axis invasion of Yugoslavia in April 1941, before turning to an understanding of the Chetnik leadership’s role in engaging in the civil war. As the civil war unfolded, so did the collaboration agreements with the German and Italian occupation authorities which, in turn, aided the Chetniks’ goals of creating a “Greater Serbian” project and the targeting of outgroup peoples.