What acts as the source of all American anti-monopoly laws?

The Sherman Act serves as the foundational source of all American anti-monopoly laws. Enacted in 1890, it was the first federal legislation to address anti-competitive practices and monopolistic behaviors directly. The primary purpose of the Sherman Act is to prevent business practices that unfairly restrain trade or commerce among several states or with foreign nations. It established two main offenses: contracts, combinations, or conspiracies that restrain trade and the actual establishment of monopolies.

This act is significant because it laid the groundwork for future legislation and enforcement around competition, leading to the creation of more specific laws such as the Clayton Act, which addresses practices that could lead to monopolization and unfair competition. Additionally, the Federal Trade Commission Act established the Federal Trade Commission (FTC) to enforce compliance with these laws, but these follow the principles set forth in the Sherman Act. The term "Antitrust Act" is often used colloquially to refer to these laws collectively, but it doesn’t denote a singular piece of legislation in the same way that the Sherman Act does. Thus, the Sherman Act is the key legislative act that initiated American anti-monopoly law and its principles.