what started ww2

World War II began on September 1, 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. The United Kingdom and France declared war on Germany on September 3, 1939, in response to the invasion. However, the causes of World War II are complex and multifaceted. The deteriorating global situation in the 1930s, with Nazi Germany annexing Austria and Czechoslovakia and conquering Poland, Belgium, the Netherlands, and France, intensified the debate in the United States over whether American interests were better served by staying out or getting involved. The urgency of the situation intensified the debate in the United States over whether American interests were better served by staying out or getting involved. Interventionists believed the United States did have good reasons to get involved in World War II, particularly in Europe, as the democracies of Western Europe were a critical line of defense against Hitler’s fast-growing strength.