 The Germans followed up Case White with a further offensive , codenamed " Case Black " , whose objectives were the " disarming of all Chetniks and the destruction of all Partisans in Montenegro and Sandžak " , to secure important bauxite , lead , and chromium mines . According to Tomasevich , the main reasons for the offensive were the threat of an Allied landing in the Balkans and the need to eliminate resistance groups that could assist the Allies . In early May 1943 , the Germans entered the Sandžak and eastern Montenegro area . Đurišić withdrew to Kolašin with about 500 fighters and joined forces with Serbian Chetniks commanded by Dragutin <unk> . 
