Postponing Operation Barbarossa, Nazi Germany simultaneously attacked Yugoslavia and Greece on 6 April 1941, Orthodox Easter Sunday. The Luftwaffe bombed Belgrade, killing between 3,000 and 4,000 people. Within a week, Germany, Bulgaria, Hungary and Italy invaded Yugoslavia, and the government was forced to surrender on 17 April. Parts of Yugoslavia were annexed by Italy, Bulgaria, Hungary and Germany. The remaining parts were governed by two German-controlled puppet governments, the Independent State of Croatia and the Serbian Government of National Salvation.