Recently we have looked at the problem of market structure, and saw that sometimes markets are not competitive. When this happens there may be a role for government policy in correcting possible problems. A few firms supply all output. One firm supplies all output.
Key factor is barriers to entry.
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.