In the 1930s, Germany and Japan aggressively expanded their territories, with Hitler aiming for land to support a growing population and violating the Treaty of Versailles. Hitler's strategic alliances, including with Italy, and his invasion of Austria and Czechoslovakia led to increased tensions with Western powers, ultimately resulting in the Nazi-Soviet non-aggression pact. This agreement allowed Hitler to invade Poland on September 1, 1939, prompting Britain and France to declare war on Germany two days later.