Final answer:
The law used to dissolve John D. Rockefeller's Standard Oil Trust into competing companies in 1911 was the Sherman Antitrust Act.
Step-by-step explanation:
The law used to dissolve John D. Rockefeller's Standard Oil Trust into competing companies in 1911 was the Sherman Antitrust Act.
This act passed in 1890, was the first U.S. antitrust law and aimed to limit the power of large trusts and monopolies. In an early demonstration of the law's power, the U.S. Supreme Court upheld the government's right to break up Standard Oil, which had controlled about 90% of the country's oil refining, into 34 independent firms.
The Sherman Antitrust Act was a crucial step in preventing the concentration of power in the hands of a few industrialists, promoting competition, and ensuring a more level playing field in the economy.
Therefore, the law is the Sherman Antitrust Act.