Emergence of USA as a strong country: The Great Economic Depression that affected USA in 1927 brought in many changes in the politics of USA. USA had helped the Triple Entente with money and soldiers. In 1929, USA. experienced stagnation in economic development. As a result, output dropped in automobile and agriculture. There was also drop in the output of consumer durables manufacturing, mining, ship building, and many other industries. This economic crisis led to changes in the politics.

During the Second World War, Japan attacked Pearl harbor, the military base of USA. This made USA to enter the war in favour the allied forces. The President Roosvelt made people to be ready for war. He encouraged women to work in public spear. USA won the war. It also helped the establishment of UNO during the war and later provided its support to it. USA has emerged as a powerful country after 1945. With the end of Cold War, USA has become the only Super Power of the world.