Explanation:

Prior to invading Poland, Germany had made a deal with the Soviet Union. After Poland was defeated, the country was divided up between Germany and the Soviet Union. Even though France and Great Britain declared war on Germany in 1939, there wasn't a lot of fighting at first.

It was in April of 1940 when Germany went on the attack again. On April 9, 1940 Germany invaded Norway and Denmark. Soon after that, they invaded the Netherlands, Belgium, and France. On June 22, 1940 Germany signed an agreement that gave them control of the Northern half of France.
Up until this point in the war, the Soviet Union had been allied with Germany. However, on June 22, 1941 Germany invaded the Soviet Union. Now the Soviet Union was on the side of the Allies.