[tzs]

That's not the whole story in the United States. Antitrust law prohibits monopolization, which is monopoly power couple with anticompetitive practices, but it also prohibits various practices from companies that do not have monopoly power.

For example the Sherman Act prohibits attempted monopolization. You run afoul of that for anticompetitive conduct and a specific intent to monopolize if there is a dangerous probability that will achieve monopoly power.

The Clayton Act added restrictions on price discrimination, exclusive dealing, tying, and mergers and acquisitions that substantially reduce competition or tend to create monopolies.