A lot of Communist countries placed embargoes on American goods, and refused to do business with the US, not the other way around. Communist regimes needed to restrict economic dealings with the US and other Western, capitalist nations in order to preserve their own, fragile and deeply-flawed economic policies. The Berlin Wall, for example, was not constructed solely for the purpose keeping the population inside East German control. It was primarily to prevent a free-flow of Western goods and currency, which would destabilize the Communist economic structure.
Communist countries failed (and - without exception - will always fail) because Communism is fatally flawed. It may sound good on paper, but in practice, there are too many real-life issues and circumstances (including inevitable human corruption and abuses of power) that necessarily prevent it's utopian vision from ever being realized.