The following month, in order to drive home the advantage that this measure created, the movement’s Operational Staff decreed that all new recruits must undergo political instruction.100 Further, given that the Partisans’ burgeoning combat effectiveness increasingly enabled them to protect the population against the Ustasha, the Ustasha’s murderous persecution of the Serbs was increasingly likely to feed the fl ow of Partisan volunteers. The dire state of Croatian admin- istration, and the Germans’ own thinly-stretched manpower, made it harder still for the Germans to keep the Ustasha’s barbaric conduct in check. In June and July’s German-led Operation Kozara, for instance, the SS reported that the Ustasha was killing the old, orphaned, and chronically ill among the deportees. In August, the Ustasha was able to wage a campaign of mass killing in the Syrmian lowlands by taking advantage of the absence of German troops busily combating Partisans in the Fruška mountains.101 Meanwhile, German army commanders responded to the burgeoning Partisan threat by reasserting their faith in “systematic and organized”
