Tank Battle: Blitzkrieg recreates the opening battles of World War II. On September 1, 1939, the German army advanced into Poland. Two weeks later, the Soviets also invaded Poland, and the Polish army was crushed by October 6. In the following months, the Germans expanded their influence throughout Europe with further invasions of Denmark and Norway. On May 10, 1940, the Battle of France began after the German army entered Belgium, the Netherlands, and Luxembourg. Within weeks, the French army was forced to surrender, and the British army retreated to Dunkirk.