On 6 April 1941, the Axis powers, consisting of German, Italian, Hungarian and Bulgarian forces invaded Yugoslavia from all sides.

[2] In accordance with Italian and German Nazi policies, racial laws were introduced against the NDH's minority populations, which included the formation of concentration camps.

Seeking to disrupt Ustaše rule and the German war effort, they raided and shot soldiers or police officers and sabotaged railroad lines.

The largest single massacre occurred on the night of 4-5 September 1942 when more than a thousand prisoners were taken to the Orthodox cemetery of Mitrovica.

The massacre ended sometime in the early morning and bodies were dumped in mass graves which had been dug by other captured Serbs.

Whereas the Ustaše applied violence indiscriminately, the Wehrmacht enacted reprisal shootings according to the German code of conduct set out by Heinrich Himmler.