What were the consequences of World War II for the United States?
Coming out of World War II, the primary consequence was the rise of the United States as one of two dominant world powers along with the Soviet Union. The United States and Soviet Union had the largest economic growth from the war time economic boom and their markets were least affected by the disbursement of resources and destruction of natural assets, unlike continental Europe which suffered greatly in the post-war environment.
As the United States and Soviet Union expanded their power they likewise expanded their influence with the United States overseeing much of the rebuilding effort and economic recovery in Western Europe through the Marshall Plan and the Soviet Union bringing most of Eastern Europe into their satellite sphere of influence. This would set the stage for the Cold War which would play on in the background as the United States saw extreme economic growth and social development that would lead to the often fondly remembered 1960's. With the fall of the Soviet Union in 1991, the long competition between the United States and USSR ends with the United States as the world's leading power, a position it attained after 50 years of consistent post-war success.
The Allied Powers also go on to create the United Nations of which the United States will be a leading influence as it helps to shape a post-colonial world and return sovereignty to many of the previously European held countries. Because the United States had no real colonies to divest (save the Philippines but that in and of itself is an entirely different story) they suffered the least from the loss of colonial influence.