In April 1941, the Axis powers invaded and soon occupied Yugoslavia. When a Yugoslav defeat seemed imminent, the Communist Party of Yugoslavia ("Komunistička partija Jugoslavije", KPJ) instructed its 8,000 members to stockpile weapons in anticipation of armed resistance. By the end of 1941, armed resistance had spread to all areas of the country except Macedonia. Building on its experience with clandestine operations across the country, the KPJ proceeded to organise the Yugoslav Partisans, as resistance fighters, led by Josip Broz Tito. The KPJ assessed that the German invasion of the Soviet Union had created favourable conditions for an uprising. On 27 June 1941, in response, the KPJ politburo founded the Supreme Headquarters of the National Liberation Army of Yugoslavia, with Tito as commander-in-chief.