1. On December 17, 1790, the United States Congress approved a plan to establish a federal district along the Potomac River, and President George Washington signed the bill into law. This would become known as the District of Columbia, and the capital city of Washington, D.C. would be established in this area.

2. In 1862, President Abraham Lincoln issued the Emancipation Proclamation, which declared that all slaves in Confederate-held territory were now free. The announcement was made on December 17, 1862, and went into effect on January 1, 1863.

3. On December 17, 1903, Orville and Wilbur Wright succeeded in the first powered flight of an airplane at Kitty Hawk, North Carolina. The Wright Brothers' accomplishment would change the world of transportation forever.

4. In 1973, Congress passed the Endangered Species Act, which protected species that were at risk of becoming extinct. This act helped to save many endangered animals, and has become an important tool for conservationists.

5. On December 17, 2010, the "Don't Ask, Don't Tell" policy was repealed, allowing openly gay individuals to serve in the United States military. This marked a significant shift in military policy and civil rights for the LGBTQ+ community.