The two sides were both wearing down and essentially in a stalemate, particularly after the fall of Russia. The entrance of a fresh, new country---and one with substantial resources---breathed new life into the allies.
U.S, & Russia.
USA
Become an ally of the soviet union-----APEX
The USA and Russia were the two main superpowers (although Russia did not have much of a Navy at the end of the war, it was mainly a air and land based superpower). England was still a superpower, but, it was in decline and many of it's colonies would soon get their freedom. France, mostly conquered by Germany, was not a superpower, although it continued to act as though it were, and it lost most of it's colonies after the war as well.
The U.S. economy had not been destroyed by fighting during WW2.
Economic prosperity and choosing their friends well
become an international superpower later in the twentieth century.
U.S, & Russia.
The United States emerged from the war as superpower.
America and Russia.
USA
US and USSR
After the Cold War, the United States emerged as the world's leading superpower. Even as a superpower, the US cannot enforce all of its policies on the rest of the countries in the world.
After World War II, the productive capacity and technological advances gave the US a distinct advantage. It was not ravaged by the war and its infrastructure was intact.
The US turned into a superpower
Unable to tell if you are referring to The American Revolution or World War 2. The Brits retained the superpower status after the American Revolution and The War of 1812. The United Kingdom lost their superpower status after World War 2 when the US and USSR took the superpower status.
The United States and The USSR.