The Blitzkrieg, or lightning war, was a military doctrine that emphasized speed, surprise, and overwhelming force to achieve rapid victory. By utilizing coordinated attacks from tanks, infantry, and air support, the German military sought to bypass enemy defenses and strike deep into enemy territory, causing confusion and cutting off communications. This strategy was used to great effect during the invasion of Poland in 1939, and later in the invasion of France and the Low Countries in 1940, where it allowed German forces to quickly overcome their opponents and achieve rapid territorial gains.