In April 1941, the Kingdom of Yugoslavia was invaded, occupied and dismembered by the Axis powers, led by Nazi Germany. A fascist puppet state known as the Independent State of Croatia ("Nezavisna država Hrvatska" or NDH) was proclaimed on 10 April, and included almost all of modern-day Croatia, all of modern-day Bosnia-Herzegovina and parts of modern-day Serbia. Led by the Croatian nationalist Ustaše movement, one of the NDH's policies was to eliminate the state's ethnic Serb population with mass killings, expulsions and forced assimilation. Resistance movements were soon created in response to the occupation, one of which was organised by the Communist Party of Yugoslavia. Headed by Josip Broz Tito, the Party decided on 4 July to launch a nationwide armed uprising and the members of the forces under its leadership became known as Partisans; they were also referred to as the National Liberation Army of Yugoslavia. In December 1943 and January 1944, the 11th Krajina Brigade of the National Liberation Army was attacking the Germans and Ustaše in the area of Mount Kozara, in northern Bosnia, to relieve pressure from the Partisans in Banija and eastern Bosnia, where the Axis were conducting major anti-Partisan offensives.