- German troops invade Poland, starting World War II in Europe.
- In 1943, Allied leaders Winston Churchill and Franklin Roosevelt meet at the Casablanca Conference to discuss plans for invading Europe, agreeing to first invade Italy.
- In 1944, the massive Allied invasion of German-occupied Western Europe, known as Operation Overlord or D-Day, begins with the Normandy landings, marking a major turning point in the war.