Answer:
After WWII, the balance of power was split between two countries: the United States, and the Soviet Union. These two countries became the two world superpowers that would shape the geopolitics of the world in the following decades.
The United States is the capitalist country, that supports a market economy, and whose allies are located in Western Europe.
The Soviet Union is the socialist country, that supports a planned economy, and whose allies are located in Eastern Europe.
This ideological struggle also led to a military struggle in what was known was the "Cold War". Two military alliances were formed: NATO, that included the U.S. and its allies, and the Warsaw Pact, that included the Soviet Union and its allies.
With the collapse of the Soviet Union in 1991, the U.S. became victorious in this struggle, and enjoyed for a brief period, a great degree of geopolitical power as the sole superpower of the world.