April 19, 1775 - At dawn in Massachusetts, about 70 armed militiamen stood face to face on Lexington Green with a British advance guard unit. An unordered 'shot heard around the world' began the American Revolution. A volley of British rifle fire was followed by a charge with bayonets leaving eight Americans dead and ten wounded.
April 19, 1995 - At 9:02 a.m., a massive car-bomb explosion destroyed the entire side of a nine story federal building in Oklahoma City, killing 168 persons, including 19 children inside a day care center. A decorated Gulf War veteran was later convicted for the attack.
April 20, 1914 - Miners in Ludlow, Colorado, were attacked by National Guardsmen paid by the mining company. The miners were seeking recognition of their United Mine Workers Union. Five men and a boy were killed by machine gun fire while 11 children and two women burned to death as the miners' tent colony was destroyed.
April 20, 1999 - The deadliest school shooting in U.S. history occurred in Littleton, Colorado, as two students armed with guns and explosives stormed into Columbine High School at lunch time then killed 12 classmates and a teacher and wounded more than 20 other persons before killing themselves
April 21, 1836 - The Battle of San Jacinto between Texans led by Sam Houston and Mexican forces led by Santa Anna took place near present day Houston. The Texans decisively defeated the Mexican forces thereby achieving independence.
April 21, 1918 - During World War I, the Red Baron (Manfred von Richtofen) was shot down and killed during the Battle of the Somme. He was credited with 80 kills in less than two years, flying a red Fokker triplane. British pilots recovered his body and buried him with full military honors.
April 22, 1889 - The Oklahoma land rush began at noon with a single gunshot signaling the start of a mad dash by thousands of settlers. The were seeking to claim part of nearly two million acres made available by the federal government. The land originally belonged to Creek and Seminole Indian tribes.
April 23rd - Established by Israel's Knesset as Holocaust Day in remembrance of the estimated six million Jews killed by Nazis.
April 24, 1800 - The Library of Congress was established in Washington, D.C. It is America's oldest federal cultural institution and the world's largest library. Among the 145 million items in its collections are more than 33 million books, 3 million recordings, 12.5 million photographs, 5.3 million maps, 6 million pieces of sheet music and 63 million manuscripts. About 10,000 new items are added each day.