The Second World War began when Britain declared war on Germany following the latter country’s invasion of Poland in September 1939. The war in Europe quickly escalated, with the Germans next invading France, and Italy signing a pact with Hitler.
Public feeling in America was that the war was a European affair, and that it did not affect them. The U.S. government also decided that America would stay out of the war. However, there was concern about Japanese activities in Asia after that country invaded several others in the region.
Tension between the two countries had remained high since the end of World War I. After that war, Japan had been forced to disarm, and under international treaties had to keep their naval power at roughly two-thirds of that of America. This was a continuing source of resentment to the Japanese.
The Japanese unilaterally broke the disarmament treaty in 1934 and began to expand their naval power. The Japanese motivation for territorial expansion was their rising demand for energy, all of which the country had to import. To achieve their aims, they felt they needed a strong navy.
JOINT RESOLUTION Declaring that a state of war exists between the Imperial Government of Japan and the Government and the people of the United States and making provisions to prosecute the same.
Whereas the Imperial Government of Japan has committed unprovoked acts of war against the Government and the people of the United States of America:
Therefore be it Resolved by the Senate and House of Representatives of the United States of America in Congress assembled, That the state of war between the United States and the Imperial Government of Japan which has thus been thrust upon the United States is hereby formally declared; and the President is hereby authorized and directed to employ the entire naval and military forces of the United States and the resources of the Government to carry on war against the Imperial Government of Japan; and, to bring the conflict to a successful termination, all the resources of the country are hereby pledged by the Congress of the United States.
Outbreak of War
When the Japanese launched their surprise attack on Pearl Harbor, the U.S. could no longer stay at peace, and immediately declared war on Japan. Churchill followed the American declaration of war against the Japanese with a British declaration of war on that country as well.
It was almost inevitable that America would be drawn into the war in Europe once Britain had allied with them against the Japanese. Initially, the Americans were reluctant to send troops to Europe, and instead supplied much needed armaments to the British forces.
However, as the Germans invaded more and more European countries, the U.S. government and military leaders realized that they had to be stopped and began sending troops to Britain.