Here are 20 significant events that occurred on April 18th throughout history, listed in chronological order:

1. 1775: The Midnight Ride of Paul Revere took place during the American Revolutionary War.
2. 1831: The University of Alabama was founded.
3. 1906: The devastating San Francisco earthquake struck, resulting in widespread destruction.
4. 1923: The Yankee Stadium, home to the New York Yankees baseball team, opened.
5. 1934: The first laundromat (self-service laundry) in the United States opened in Fort Worth, Texas.
6. 1942: The Doolittle Raid, an air raid by the United States on Tokyo during World War II, occurred.
7. 1946: The League of Nations dissolved, making way for the United Nations.
8. 1949: The Republic of Ireland was established.
9. 1955: Physicist Albert Einstein passed away in Princeton, New Jersey.
10. 1979: The SALT II arms limitation treaty was signed by the United States and the Soviet Union.
11. 1983: A suicide bombing destroyed the United States embassy in Beirut, Lebanon.
12. 1988: The United States launched Operation Praying Mantis against Iranian naval forces.
13. 1988: The United States launched Operation Golden Pheasant in Honduras.
14. 1989: The tragic Hillsborough disaster occurred during a football match in Sheffield, England.
15. 1996: Major League Soccer (MLS) made its debut with its first match.
16. 2007: The Supreme Court of the United States upheld the Partial-Birth Abortion Ban Act.
17. 2014: The United States announced sanctions against Russian individuals and companies.
18. 2019: The Mueller Report, which investigated Russian interference in the 2016 U.S. presidential election, was released.
19. 2020: NASA's space probe, the Mars InSight lander, recorded seismic activity on Mars for the first time.
20. 2021: President Joe Biden announced the withdrawal of all U.S. troops from Afghanistan by September 11, 2021.

These events highlight a diverse range of historical, political, and scientific milestones that have occurred on April 18th over the years.