Why did the United States and the USSR distrust each other after the war?

Communism constituted enormous thread for the West from the very beginning (Communist Manifesto, 1848). In 1848 we have many popular insurrections against monarchy and aristocracy and these elites felt rightfully threatened. At that time Communism started as a theory, a doctrine. The first political expression of these ideas appeared in Paris 1871 and then in Boshevik revolution in 1917. It was USSR that institutionalized Communist idea. USSR was a visible example that idea of  Communism can be realited, that Communist regime is possible. Western elites were afraid of that. Communism was a threat for Catholic church as well. Communism was able mobilize masses and Soviet victory in WW II enabled Soviets to promote there regime. So United States did not confront a new enemy, but an old one. It was a threat that existed long time before WW II.

Explanation: Soviets viewed Americans as the main representant of capitalism so for them it was an enemy no.1.