1. On March 15, 1869, the National Museum of American History was founded in Washington D.C. It is one of the largest collections of American history in the world.

2. In 1878, Alexander Graham Bell demonstrated the telephone to President Rutherford B. Hayes on March 15th. This event is considered one of the major milestones in the development of communication technology.

3. The first-ever Cherry Blossom Festival was held on March 15, 1935, in Washington D.C. The festival has since become an annual tradition, attracting thousands of visitors from around the world each year.

4. On March 15, 1977, the Washington D.C. City Council passed a law prohibiting discrimination based on sexual orientation. Washington D.C. was one of the first cities in the United States to pass such a law.

5. March 15, 1985, marked the first-ever meeting between a U.S. president and a Soviet leader held in Washington D.C. President Ronald Reagan and Soviet leader Mikhail Gorbachev met to discuss arms control and other issues during the two-day summit.