However, Italy's conquests were always heavily contested, both by various insurgencies (most prominently the Greek resistance and Yugoslav partisans) and Allied military forces, which waged the Battle of the Mediterranean throughout and beyond Italy's participation. German and Japanese actions in 1941 led to the entry of the Soviet Union and United States, respectively, into the war, thus ruining the Italian plan of forcing Britain to agree to a negotiated peace settlement. Ultimately the Italian empire collapsed after disastrous defeats in the Eastern European and North African campaigns. In July 1943, following the Allied invasion of Sicily, Mussolini was arrested by order of King Victor Emmanuel III, provoking a civil war. Italy's military outside of the Italian peninsula collapsed, its occupied and annexed territories falling under German control. Italy capitulated to the Allies on 3 September 1943.