How [or why] did the U.S. and the Soviet Union become cold war adversaries?

the united states and soviet union both emerged as superpowers following world war ii, and both wanted to spread their influence around the world. two differing ideologies - communism and democracy. since it was not practical or preferable to fight a 'hot' war to decide who was king, the two sides settled into a cold war in which other countries were used as pawns in their power game, spying on each other, the space race, the nuclear and conventional arms race, etc