The major global conflict sparked by the invasion of Poland in 1939 was World War II. On September 1, 1939, Nazi Germany, led by Adolf Hitler, invaded Poland, prompting Britain and France to declare war on Germany two days later. This invasion was a significant escalation in Hitler’s aggressive expansionist policies, violating agreements and norms established after World War I. The conflict rapidly expanded as Axis Powers sought dominance across Europe and later in Asia. The war eventually involved numerous countries worldwide and resulted in unprecedented devastation, leading to significant changes in the geopolitical landscape and the establishment of international organizations in its aftermath.