When Did America Enter WW2? Why Did Japan Attack?

When Did America Enter WW2? A Not-So-Straightforward Answer

When Did America Enter WW2? America officially only entered World War 2 two years into the war on December 8, 1941, when all but one member of Congress passed the motion one day after the attack on Pearl Harbor in Hawaii. Although America formally maintained neutrality up until that moment, the U.S. has long been involved in the war, providing support to the Allies.

When Did America Enter WW2? – Not That Neutral

In the first two years of the war, America remained politically neutral, but president Franklin was working hard to prepare the Americans for what he regarded to be an inevitable conflict. He felt that the war was threatening U.S. security and tried to find ways to help the European Allies without being formally involved in the war. He persuaded Congress in November 1939 to repeal the arms embargos that were part of the neutrality law and pass the Fourth Neutrality Act, which allowed him to trade arms with countries whose defence he would seem to be vital to the security of the United States. The U.S. would also provide its air force and navy to “escort” British convoys that transported supplies “leased” from America to protect them from enemy submarines. The U.S. military was also deployed to replace British forces in Iceland after the British invasion there.

When Did America Enter WW2? – Why Japan Attacked

In coordination with the Dutch and the British, the U.S. was running a very successful oil embargo against Japan. At that time the Japanese were advancing on China and French Indochina and, because they imported 90% of their oil, they became desperate. A lack of oil threatened to end all of their war efforts and as they were refusing America’s demands to stop fighting China, the Japanese decided that war with America was inevitable, their only hope was to attack first.

So when did America enter WW2? Officially after the bombing of Pearl Harbor, but the United States had been moving toward allianceship with Allied Powers for years.

This article is part of our larger educational resource on World War Two. For a comprehensive list of World War 2 facts, including the primary actors in the war, causes, a comprehensive timeline, and bibliography, click here.

This article is also part of our larger selection of posts about the Pearl Harbor attack. To learn more, click here for our comprehensive guide to Pearl Harbor.