The United States was in a state of serious economic depression before the start of World War 2. Americans were suffering greatly; there was little or no food, and most were jobless especially the minority. America was struggling and no inroads were made in any field whatsoever. The United States had too many problems at home and had no real passion for exerting its influence overseas. It was only with the out break of war did America fully recover from its worst depression in history. The war kick started the economy. A country at war needed supplies; guns, tanks, ships, aircraft, food etc. People were able to find jobs and the economy rose and stabilized. John Maynard Keynes said that it was possible to prevent sharp swings in the business cycle thus preventing another depression through monetary and fiscal manipulation. This theory by Keynes was a lesson the American government learnt and the United States was able to maintain its economic power after the war.

With economic power came military power. During the war America was able to advance technologically in nearly all fields. Planes were build that traveled longer distances and thus kick starting the aviation industry. Penicillin was invented, trucks carried heavier loads, new industries sprung up and peoples were richer and America became a powerhouse technologically and economically. This power enabled the US government to exert its influences over much of the western world.

The Allies were not doing too well during World War 2 and it only started winning after America joined in. once it was officially in the war, the America government took a leadership position in defeating the Germans. The Americans with the British and Soviets were responsible for creating the UN and also split the land of the defeated Germans among themselves. The Yalta conference was a big turning point in Soviet US relations.