The primary purpose of the Antitrust Act of 1890, also known as the Sherman Antitrust Act, was to prohibit monopolistic business practices and promote fair competition in the marketplace. It aimed to prevent corporations from engaging in anti-competitive behavior that could stifle competition and harm consumers. The act made it illegal to restrain trade or commerce through monopolies or conspiracies in restraint of trade. Enforcement of the act began in earnest in the late 19th century and into the 20th century, leading to significant legislation that shaped the legal landscape of American business practices and protections for consumers.