1. July 21, 1861: The First Battle of Bull Run
On this day, the First Battle of Bull Run took place, which was the first major land battle of the American Civil War. Confederate forces led by General P.G.T. Beauregard and Union forces led by Brigadier General Irvin McDowell clashed in what would be a devastating day for the Union army, leading to their eventual retreat.

2. July 21, 1969: The Moon landing
On July 21, 1969, astronaut Neil Armstrong famously became the first human being to set foot on the moon. Armstrong's famous words, "That's one small step for man, one giant leap for mankind," will forever be remembered as a milestone achievement for human exploration.

3. July 21, 1972: Washington D.C. Metropolitan Police Department established
The Washington D.C. Metropolitan Police Department, also known as the MPD, was established on this day in 1972. The department is responsible for ensuring the safety and security of the city's residents and visitors, and operates in all eight wards of the District of Columbia.

4. July 21, 1986: John Poindexter and Oliver North testify before Senate
On July 21, 1986, John Poindexter and Oliver North testified before the Senate regarding their involvement in the Iran-Contra affair. The Iran-Contra scandal involved the United States' secret sale of weapons to Iran, which was then used to fund the Contras in Nicaragua. The scandal rocked the Reagan administration and had far-reaching political implications.

5. July 21, 2007: The Smithsonian Folklife Festival
The Smithsonian Folklife Festival takes place annually on the National Mall in Washington D.C., and on July 21, 2007, the festival celebrated its 41st year. The festival showcases the diverse cultures of the United States and the world through music, dance, crafts and food.