What incident is widely considered to have ignited World War II?

The incident that is widely recognized as igniting World War II is the invasion of Poland by Germany on September 1, 1939. This act of aggression marked the start of the war in Europe, prompting Britain and France to declare war on Germany shortly thereafter.

Prior to this invasion, tensions had been escalating in Europe due to Germany's expansionist policies under Adolf Hitler, but it was the invasion of Poland that directly led to the outbreak of global conflict. Germany's attack not only violated Poland's sovereignty but also showcased the failure of appeasement policies that had been employed by other nations to deal with Hitler’s ambitions.

The other events mentioned, while significant in history, did not directly trigger World War II. The bombing of Pearl Harbor, for example, brought the United States into the war, but it occurred much later in December 1941. The assassination of Archduke Francis Ferdinand happened in 1914 and is related to the start of World War I. The sinking of the Lusitania, which contributed to anti-German sentiment in the United States before World War I, occurred in 1915 and also does not pertain to World War II's initiation. Thus, the invasion of Poland stands as the key incident that ign