In what year did World War II begin?

World War II began on September 1, 1939, when Germany invaded Poland. This invasion led Britain and France to declare war on Germany shortly thereafter, marking the official start of the conflict. The year 1939 is significant because it signifies the escalation of tensions that had been building throughout the 1930s due to various factors, including the rise of totalitarian regimes and the failure of the League of Nations to maintain peace.

The other years mentioned in the options correspond to different significant events within World War II. For instance, 1941 is notable for the Japanese attack on Pearl Harbor and Germany's invasion of the Soviet Union, while 1945 marks the end of the war with the surrender of Germany in May and Japan in September. The year 1935 does not hold any critical significance relating to the start of the war, as it was before the major escalation of conflict in Europe. Thus, 1939 is the accurate year representing the commencement of World War II.