In September 1939, Germany invaded Poland starting World War 2 in Europe. Germany used blitzkrieg tactics to quickly defeat Poland. In 1940, Germany invaded Denmark, Norway, the Netherlands, Belgium, and France, pushing the British forces back to Dunkirk. Italy then joined Germany in invading France, leading to France's defeat in June 1940. Britain stood alone against Germany until June 1941 when Germany invaded the Soviet Union. Japan, seeking resources, attacked the US naval base at Pearl Harbor in December 1941, bringing the US into the war. The US and allied forces began to turn the tide against Germany and Japan in major battles like Stalingrad, North Africa, and the Coral Sea in 1942.