The statement that is not one of the major events of World War II prior to December 1941 is:
The United States declared war as a result of Germany's invasion of Poland.
This is incorrect because the United States did not declare war on Germany immediately following the invasion of Poland in September 1939. The U.S. remained neutral for much of the early part of the war, only entering the conflict after the Japanese attack on Pearl Harbor in December 1941. The other statements refer to significant events that occurred before the U.S. entry into the war.