On December 7, 1941, the Japanese attacked the U.S. Pacific naval fleet anchored at Pearl Harbor, Hawaii, and destroyed battleships, fighter jets, and thousands of American lives. The next day, President Franklin D. Roosevelt, known as FDR, asked Congress to acknowledge the fact that since the Pearl Harbor attack, the U.S. had been at war with the empire of Japan. He said:

FDR asking Congress to declare war on Japan.

Yesterday, December 7, 1941—a date which will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan. …I ask that the Congress declare that since the unprovoked and dastardly attack by Japan on Sunday, December 7, 1941, a state of war has existed between the United States and the Japanese Empire.

Congress officially declared war on Japan that day, December 8, 1941. Three days later, on December 11, Germany declared war on the U.S. This was not completely unexpected: When Germany, Japan, and Italy signed the Tripartite Pact in 1940, they each pledged to go to war if any nation declared war on one of them. But when Adolf Hitler, the fascist leader of Germany, gave his speech declaring war on the U.S., he gave a different reason for doing it: He blamed FDR for starting the war. He said: 

Adolf Hitler telling Germany it is at war with the U.S.

And now let me speak about another world, one that is represented by [FDR], who likes to chat nicely at the fireside while nations and their soldiers fight in snow and ice: above all, the man who is primarily responsible for this war. Why has this man developed such a fanatic hostility against a country that, in its entire history, had never harmed either America or him? …Despite years of intolerable provocations by President Roosevelt, Germany and Italy sincerely and very patiently tried to prevent the expansion of this war and to maintain relations with the United States. But as a result of his campaign, these efforts have failed.

…Faithful to the provisions of the Tripartite Pact of September 27, 1940, Germany and Italy accordingly now regard themselves as finally forced to join together on the side of Japan in the struggle for the defense and preservation of the freedom and independence of our nations and realms against the United States of America and Britain.

Hitler's accusations were meant to humiliate the U.S. and put the blame for any bloodshed to come squarely onto FDR. FDR was not intimidated. The U.S. quickly declared war on Germany on the same day, December 11, 1941. Now the U.S. was involved in a world war on two fronts, Europe and Asia, and Americans were resolved to win them both. In this lesson, you will learn about each.