How did the relationship between the u. s. and the soviet union change after wwii?

U.S.-Soviet Alliance, 1941–1945. Although relations between the Soviet Unionand the United States had been strained in the years before World War II, the U.S.-Soviet alliance of 1941–1945 was marked by a great degree of cooperation and was essential to securing the defeat of Nazi Germany.

i know this cause i took it 2 years ago so yea hope this helped
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The relationship between the u.s. and the Soviet Union changed after WWII when the soviet union began to become more dominant. they started advancing faster than other countries, and the u.s. took it as a threat. the u.s. was also against communism, and the soviet union wanted to spread it. 

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