1. On April 12, 1861, Confederate forces bombarded Fort Sumter in South Carolina, marking the beginning of the Civil War. Although this event took place in South Carolina, it had a significant impact on the District of Columbia, which served as the capital of the Union throughout the war.

2. On April 12, 1862, Union troops under the command of General George McClellan began their siege of Yorktown, Virginia, during the Peninsula Campaign of the Civil War. This campaign, which aimed to capture Richmond, Virginia, the capital of the Confederacy, also had significant implications for Washington, DC.

3. On April 12, 1945, President Franklin D. Roosevelt died of a cerebral hemorrhage at his retreat in Warm Springs, Georgia. Roosevelt's death shocked the nation and led to the swearing-in of Vice President Harry S. Truman as president, which took place in the District of Columbia.

4. On April 12, 1961, Soviet cosmonaut Yuri Gagarin became the first human to travel into space, orbiting the earth aboard the Vostok 1 spacecraft. This historic achievement sparked the "space race" between the United States and the Soviet Union, which played out in various ways in the District of Columbia throughout the 1960s and 1970s.

5. On April 12, 1981, the space shuttle Columbia became the first reusable spacecraft to launch into space, carrying two astronauts into orbit around the earth. This event marked a significant milestone in the history of space exploration and had implications for the space program at NASA's Goddard Space Flight Center, located in Maryland, just outside of the District of Columbia.