On this day in 1999, two teenage gunmen kill 13 people in a shooting spree at Columbine High School in Littleton, Colorado, south of Denver.

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The great San Francisco earthquake killed 3,000 people, Paul Revere's midnight ride took place, physicist, Albert Einstein died, and play ball began a Yankees and Red Sox game for the first time in This Day in History video. The date is April 18th. Paul Revere's ride resulted in the battles of Lexington and Concord and signaled the beginning of the Revolutionary War.

Many historical events occurred on April 4th, and Russ Mitchell recaps them in this video clip from This Day In History. President William Henry Harrison became the first US President to die while in office when his cold turned into pneumonia. Congress passed and authorized what would become known as the American flag, with 13 strips, and then 20 stars with a blue background. Each state that would be added would add another star to the flag. Also, the first Mexican American, Henry Cisneros, became mayor of a major city, which was Texas. On Martin Luther King Jr.'s Memphis hotel balcony, James Earl Ray assassinated King.

Jesse James, one of the most wanted bank and train robbers was shot in the back by one of his gang members for the reward on April 3rd. Russ Mitchell recaps this and other events that occurred on April 3rd in this video clip from This Day In History. The day before Martin Luther King Jr. was assassinated, April 3, he gave his famous mountain speech. A resolution to end the Gulf War was passed by the UN Security Council, and the fasted mail service at the time in the west, The Pony Express, began on this day.

LSD the hallucinogenic is discovered, Lenin returns to Russia during the Russian Revolution, Mick Jagger and the Rolling Stones release their first album, and Wayne Gretzky retires from hockey in This Day in History video. The date is April 16th. Vladimir Lenin, a Russian revolutionary, is famous for initiating what many call the October Revolution.

The polio vaccine by Jonas Salk begins human testing, Captain John Smith lands in Jamestown, Lucy from I Love Lucy dies, and the Treasury unveils a new $50 bill in This Day in History video. The date is April 26th. Lucille Ball and Desi Arnaz known as Ricky Ricardo became famous in I Love Lucy.

On this day in 1916, on Easter Monday in Dublin, the Irish Republican Brotherhood, a secret organization of Irish nationalists led by Patrick Pearse, launches the so-called Easter Rebellion, an armed uprising against British rule. Assisted by militant Irish socialists under James Connolly, Pearse and his fellow Republicans rioted and attacked British provincial government headquarters across Dublin and seized the Irish capital's General Post Office. Following these successes, they proclaimed the independence of Ireland, which had been under the repressive thumb of the United Kingdom for centuries, and by the next morning were in control of much of the city. Later that day, however, British authorities launched a counteroffensive, and by April 29 the uprising had been crushed. Nevertheless, the Easter Rebellion is considered a significant marker on the road to establishing an independent Irish republic.