In 1999, the Columbine High School massacre took place in Colorado as two students, Eric Harris and Dylan Klebold, shot and killed 12 classmates and one teacher before taking their own lives.
1792: France declared war on Austria, marking the start of the French Revolutionary Wars.
1861: Col. Robert E. Lee resigned his commission in the United States Army. (Lee went on to command the Army of Northern Virginia, and eventually became general-in-chief of the Confederate forces.)
1863: President Abraham Lincoln signed a proclamation admitting West Virginia to the Union, effective in 60 days (on June 20, 1863).
1945: During World War II, allied forces took control of the German cities of Nuremberg and Stuttgart.
1972: Apollo 16's lunar module, carrying astronauts John W. Young and Charles M. Duke Jr., landed on the moon.