In which year did World War II begin?

World War II began on September 1, 1939, when Germany invaded Poland, which catalyzed the conflict between various countries around the globe. This event marks the official start of the war, leading to the involvement of major powers such as the United Kingdom and France, who declared war on Germany shortly afterward.

The other options refer to significant events but do not represent the start of the war. For instance, 1935 is notable for various events leading up to the war, but not the war itself. The year 1941 includes the United States' entry into the war following the attack on Pearl Harbor, while 1945 marks the end of World War II with the unconditional surrender of Germany in May and Japan in September. Hence, 1939 is the year that correctly identifies when World War II officially began.