Monopolies (both actual and defacto) exist when one institution controls the access to something else, generally a commodity, information, or a service. In the absence of external controls, the institution can (and almost inevitably does) then set the price, determine the attributes of what they’re selling, and, even, who’s eligible to acquire what’s being sold. The key to the idea is control. A monopoly that is actually being regulated does not have the power that an unregulated one has, a power that is generally misused.
How it works
Monopolies usually happen when an business or individual acquires a new resource that is in high demand. before government regulations, or public opinion can challenge the companies selling their product, the monopoly on that product has already occurred.