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 Keserović.