1. Gettysburg Address Monument was dedicated on July 21, 1869. The monument, located in Gettysburg National Cemetery, was erected to commemorate President Abraham Lincoln and his famous Gettysburg Address, which he delivered during the Civil War.

2. Pennsylvania founded on July 21, 1681, when King Charles II of England granted William Penn a charter for a tract of land in America. Penn named his new colony "Pennsylvania," which means "Penn's Woods."

3. On July 21, 1877, the Great Railroad Strike began in Martinsburg, West Virginia before spreading to other states, including Pennsylvania. The strike was a large-scale labor action that involved workers from several railroad companies.

4. July 21, 1917, marked the establishment of Fort Indiantown Gap, located in central Pennsylvania. The military installation has been used for a variety of purposes over the years, including training soldiers for World War II.

5. On July 21, 1979, the Three Mile Island nuclear power plant near Harrisburg suffered a partial meltdown, which was the most significant accident in the history of the United States commercial nuclear power generating industry. The accident caused widespread concern about the safety of nuclear power and had a lasting impact on the public perception of nuclear energy.