The invasion of Yugoslavia by Germany and Italy began on 6 April, simultaneously with the new Battle of Greece; on 11 April, Hungary joined the invasion. By 17 April the Yugoslavs had signed an armistice, and by 30 April all of mainland Greece was under German or Italian control. On 20 May Germany invaded Crete by air, and by 1 June all remaining Greek and British forces on the island had surrendered. Although it had not participated in the attacks in April, Bulgaria occupied parts of both Yugoslavia and Greece shortly thereafter for the remainder of the war in the Balkans.