The Chetniks were active in uprising against the Axis occupiers throughout 1941 . Following the success of the Battle of Loznica , Mihailović 's Chetniks were the first to liberate a European city from Axis control . Following this , German occupiers enacted Adolf Hitler 's formula for suppressing anti-Nazi resistance in Eastern Europe , a ratio of 100 hostages executed for every German soldier killed and 50 hostages executed for every soldier wounded . In October 1941 , German soldiers conducted two mass murder campaigns against Serbian civilians in Kraljevo and Kragujevac , with a combined death toll reaching over 4,500 civilians , convincing Chetnik leader Draža Mihailović that killing German troops would only result in further unnecessary deaths of tens of thousands of Serbs . As a result , he decided to scale back Chetnik guerrilla attacks and wait for an Allied landing in the Balkans . While Chetnik collaboration reached " extensive and systematic " proportions , the Chetniks themselves referred to their policy of collaboration as " using the enemy " . Sabrina Ramet , a historian , has observed , " Both the Chetniks ' political program and the extent of their collaboration have been amply , even voluminously , documented ; it is more than a bit disappointing , thus , that people can still be found who believe that the Chetniks were doing anything besides attempting to realize a vision of an ethnically homogeneous Greater Serbian state , which they intended to advance , in the short run , by a policy of collaboration with the Axis forces "
Kragujevac
Kragujevac massacre
Chetniks