What marked the beginning of World War II?

The beginning of World War II is generally marked by the invasion of Poland on September 1, 1939. This event was significant as it triggered a series of declarations of war, most notably as Britain and France declared war on Germany two days later. The invasion not only marked the expansion of Nazi Germany's aggressive territorial ambitions but also signified the failure of appeasement strategies employed by Western powers. The swift and brutal military tactics used, including the Blitzkrieg strategy, set the tone for the conflict that would engulf much of the world over the following years.

In contrast, the bombing of Pearl Harbor occurred much later, in December 1941, and was a pivotal moment that brought the United States into the war, but did not initiate it. Armistice Day refers to the end of World War I and is unrelated to the onset of World War II. The attack on Germany by Allied forces took place in the later stages of the war, further underscoring why the invasion of Poland is recognized as the starting point of this global conflict.