In April 1941, the Axis powers invaded and soon occupied Yugoslavia. With the Yugoslav defeat imminent, the Communist Party of Yugoslavia ("Komunistička partija Jugoslavije", KPJ) instructed its 8,000 members to stockpile weapons in anticipation of armed resistance, which would spread, by the end of 1941 to all areas of the country except Macedonia. Building on its experience in clandestine operation 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 and its politburo founded the Supreme Headquarters of the National Liberation Army of Yugoslavia ("Narodonooslobodilačka vojska Jugoslavije") with Tito as commander in chief on 27 June 1941.