The year that marked the beginning of World War II was 1939, specifically beginning on September 1, when Germany invaded Poland. This aggressive move by Nazi Germany prompted Britain and France to declare war on Germany shortly thereafter, leading to a major global conflict that would last until 1945. The war involved numerous nations across different continents and resulted in significant geopolitical changes. The invasion was part of Adolf Hitler's broader strategy to expand German territory under the guise of protecting German-speaking people. World War II ultimately reshaped the world order, leading to the establishment of the United Nations.