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The US provided millions of dollars in weapons, armament as well as money itself to the Allied forces. But the attack on Pearl Harbor pushed us officially into the war. Because Japan went to war with us, without a declaration or any warning, first by attacking our naval base at Pearl Harbor. Most importantly, Japan attacked the US naval base at Pearl Harbor, Hawaii, without a declaration of war or any warning that hostlities were being commenced, sinking most of the battle fleet.
Research indicates that
The US stayed neutral in WWII until the US Naval Base @ Pearl Harbor, Hawaii was bombed by the Japanese on December 07, 1941. The Japanese were then enemies of the United States.
Mainly as the Japanese were misguided enough to attack Pearl Harbour and it gave the Americans the incentive they needed. A lot of people are stating that we got into the war because of Pearl Harbor because Japan attacked Pearl Harbor. Japan had been aggressive towards China and so the US halted any trade with Japan in November 1940. The bombing at Pearl Harbor was indeed a spark to the United Sates entering the second World War. America clearly felt that if we just laid down and allowed ourselves to be attacked, without a counterattack, we would be the target of many of our world enemies.
The bombing of Pearl Harbor attack is tantamount to a declaration of war. It also should be understood that while the US was technically neutral up to Pearl Harbor, they were already providing substantial aid to the Allied side. The British were being provided with arms and supplies on favorable terms, and no such supplies were being sent to the Axis.
US was already trading with other countries through the Lend-Lease Act. However, a few days after Pearl Harbor, Hitler declared war on the US, thereby putting an end to the US dilemma.
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