How is world war 2 and the cold war linked?

In world war two, Russia was our allies. They helpled us defeat the Central Powers (Germany and such) but they didnt recall their troops from foreign lands, i.e. Germany, China, Korea. So these troops, which were communist because of Russia (the Soviet Union) were seeds that changed these areas to a communist government. And well you know the rest. Eventually, its communists versus good old U.S.A.