Who was the president of the united states when world war ii began?

World War II began in 1939, and the United States joined the war in 1941 after the bombing of Pearl Harbor. By this time, President Roosevelt was already in his second term. As Commander-in-Chief of the United States military, he was a powerful leader among the Allied Forces.

Franklin D. Roosevelt, the cousin of Theodore Roosevelt, was President of the U.S. during the beginning of World War II.