Germany invaded Poland in September 1939, starting World War 2 in Europe. Using their new blitzkrieg strategy of coordinated air and land attacks, Germany quickly conquered Poland, Denmark, Norway, the Netherlands, Belgium, Luxembourg, and France in 1940. Britain resisted a German invasion attempt. In North Africa, Italy invaded Egypt while Germany sent troops led by Rommel to aid Italy against the British. By April 1941, Germany had also conquered Yugoslavia and Greece to secure its southern flank before invading the Soviet Union. Though initially successful, the German invasion of the Soviet Union eventually stalled at Moscow and Leningrad. The US aided the Allies through the Lend-Lease program and the Atlantic Charter between Roosevelt and Churchill outlined democratic principles