Neutrality and Isolationism

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Why did the United States enter World War II?

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The United States entered World War II after the Japanese Navy attacked the U.S. naval base at Pearl Harbor on December 7, 1941. This was the culmination of a long process in which Japanese imperial ambitions in the Pacific and German aggressions in Europe threatened to drag a reluctant nation...

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The United States entered World War II after the Japanese Navy attacked the U.S. naval base at Pearl Harbor on December 7, 1941. This was the culmination of a long process in which Japanese imperial ambitions in the Pacific and German aggressions in Europe threatened to drag a reluctant nation into war. In the 1930s, the United States responded to German and Japanese aggressions by maintaining its own neutrality. But President Franklin Roosevelt was always skeptical that the United States could remain aloof from the affairs of the rest of the world. In 1939, the United States began to provide military assistance to Great Britain, by then at war with Germany, on a "cash and carry" basis. Later, after Hitler overran Europe, Congress approved a "lend-lease" plan that involved massive loans of cash and war materiel to the British, the Soviet Union, and China, all of which were at war with the Axis Powers. But still the United States remained out of World War II. This changed in 1941 when, in response to the Japanese invasion of Indochina, Roosevelt ordered the cessation of oil exports to Japan, and froze Japanese assets. The Japanese then formulated a plan to attack the American naval forces based at Pearl Harbor.

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The United States entered World War Two after the Japanese navy attacked the US Navy base at Pearl Harbor, Hawaii. The sneak attack, carried out on a Sunday morning, killed more than 2,400 American servicemen and destroyed dozens of American warships, including battleships, that were moored in the harbor. Following the attack, the United States declared war on Japan, and Germany and Italy, Japan's allies in the three-part "Axis Powers" declared war on the United States. With this attack, the United States was officially at war. It is true, however, that the United States had experienced multiple German attacks on shipping in the Atlantic, and that Franklin Roosevelt was aware that an oil embargo on Japan enacted earlier in 1941 had drawn the nation to the brink of war. Moreover, the nation under Roosevelt had shed its rigid isolationist stance to essentially supply Great Britain in its struggle with the Nazis by late 1940. The nation was, in many ways, already on a war footing by 1941. But it was Pearl Harbor that removed all doubt. It was the cause of American entry into World War II.

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