The entrepreneur who gained a monopoly over the oil industry by the late 1800s was John D. Rockefeller. Here's why:
1. **Standard Oil Company:** Rockefeller founded the Standard Oil Company in 1870, which quickly grew to dominate the oil industry in the United States.
2. **Horizontal Integration:** Rockefeller used aggressive business tactics such as horizontal integration, where he acquired or eliminated competitors, to consolidate control over oil refining and distribution.
3. **Monopoly Power:** By the late 1800s, Rockefeller's Standard Oil Company controlled about 90% of the oil refineries in the U.S., giving him a near-monopoly over the industry.
4. **Anti-Trust Actions:** Rockefeller's business practices eventually led to public and government scrutiny, resulting in the breakup of the Standard Oil Company in 1911 through antitrust legislation.
In conclusion, John D. Rockefeller is the entrepreneur who gained a monopoly over the oil industry by the late 1800s through strategic business tactics and aggressive consolidation of power.
