On April 20, 1812, the fourth vice president of the United States, George Clinton, died at age 72, becoming the first vice president to die while in office.

In 1914, militia and Colorado National Guard members opened fire on an encampment of striking coal miners and their families in Ludlow, Colorado killing at least 19 people, including 12 children.

In 1971, the Supreme Court unanimously upheld the use of busing to achieve racial desegregation in schools.

In 1999, two students shot and killed 12 classmates and one teacher and injured 23 others before taking their own lives at Columbine High School, near Denver, Colorado.

In 2010, an explosion on the Deepwater Horizon oil platform killed 11 workers and caused a blowout that began spewing an estimated 200 million gallons of crude oil into the Gulf of Mexico.