At first Germany was very successful in its military operations. In less than three months (April – June 1940), Germany conquered Denmark, Norway, the Low Countries, and France. The unexpectedly swift defeat of France resulted in an upswing in Hitler's popularity and an upsurge in war fever. Hitler made peace overtures to the new British leader Winston Churchill in July 1940, but Churchill remained dogged in his defiance. Churchill had major financial, military, and diplomatic help from President Franklin D. Roosevelt in the U.S. Hitler's bombing campaign against Britain (September 1940–May 1941) failed. Some 43,000 British civilians were killed and 139,000 wounded in the Blitz; much of London was destroyed, with 1,400,245 buildings destroyed or damaged. Germany's armed forces invaded the Soviet Union in June 1941 – weeks behind schedule due to the invasion of Yugoslavia – but swept forward until they reached the gates of Moscow. Hitler had assembled more than 4,000,000 troops, including 1,000,000 from his Axis allies. The Soviets had lost nearly 3,000,000 killed in action, while 3,500,000 Soviet troops were captured in the first six months of the war. The Einsatzgruppen (Nazi mobile death squads) executed all Soviet Jews that it located, while the Germans went to Jewish households and forced the families into concentration camps for labor or to extermination camps for death.