The major global conflict triggered by the invasion of Poland in 1939 was World War II. On September 1, 1939, Germany invaded Poland, which prompted Britain and France to declare war on Germany two days later. This invasion marked the beginning of widespread hostilities that eventually engulfed multiple nations across Europe, Asia, and beyond. The war was characterized by its unprecedented scale and devastation, involving significant battles, atrocities, and the Holocaust. World War II fundamentally reshaped global politics, economies, and social structures and left a lasting legacy still felt in contemporary international relations.