On 27 March 1941, Nazi Germany's leader Hitler ordered the attack on Yugoslavia. in accordance with "Führer’s directive No. 25" which mentioned that the possession of the industrial site of the Bor copper mines was very important for military purposes. In 1943, Hungarian-Jewish forced laborers were stationed at nearby mines which covered 50 percent of the copper requirement of Nazi Germany's war industry. In the period from July 1943 to September 1944, at least 6,000 Hungarians were used. In May 1943, the total number of inmates (excluding Kapos) came to about 23,000 forced laborers from Serbia.