Answer:
Japanese aircraft carriers had approached Hawaii unnoticed.
As a result of Japan’s attack on pearl Harbor thousands of American died and the Us declared war on Japan.
The surprise attack of Japan at Pearl Harbor in Hawaii on December 7th, 1941 had killed many Americans and destroyed American ships and Airplanes along with USS Arizona, the crown of US Navy.
However, Americans have no intention in joining the Allied forces in the World War II, the drastic incident at the Pearl Harbor made them to join the war. American president FDR declared war on Japan. This made the Germany to declare war on America. The triangular declaration of war made the Americans to involve in the World War II, completely.
