What company merged approximately forty other companies to form a monopoly?

The company that famously merged approximately forty other companies to form a monopoly is Standard Oil, founded by John D. Rockefeller in the late 19th century. Through aggressive acquisition and consolidation, Standard Oil gained control over a significant portion of the oil industry in the United States. This monopolistic behavior led to significant legal challenges, culminating in the U.S. Supreme Court's decision in 1911 to break up Standard Oil into several independent companies.