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"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 regret to tell you that very many American lives have been lost. … I ask that the Congress declare that since the unprovoked and dastardly attack …, a state of war has existed between the United States and the Japanese Empire."—President Franklin D. Roosevelt, Address to Congress (1941)

Based on the quote, which statement is true about the United States' involvement in World War II after December 1941?

The United States remained isolated from the World War II conflict.
The United States used diplomacy to settle the World War II conflict.
The United States applied imperialism in World War II to gain territory.
The United States intervened in World War II by declaring war on Japan.