If no barriers to entry, no monopoly profits are possible. Firms will do everything possible to eliminate competition by price. But cheating frequently brings down these cartels. Because barriers to entry are key, a good strategy for firms is to create barriers in some way. This last is illegal in the U.S. in many cases.
Antitrust law defines certain behaviors as illegal.
Prime among them is price-fixing. But proving this in a court of law is problematic. In cases of utilities, the theory of Natural Monopoly has held that monopoly is more efficient than competition, so the government is advised to regulate instead. But recent changes in technology have opened a case for renewed competition in many of these markets. Analyze the market for health care using the categories we have developed.