I don't think America really does have a monopoly problem: once great companies like GM, GE and Sears are in trouble. You can hate Apple and Walmart, but they have been innovators. When they stop being ahead of the curve, or when they misjudge their opportunities, they will go the way of older companies that fell from a position of predominance.
The problem is when the monopolies are in bed with the government.
Symptoms: