1995: A truck packed with more than 4,000 pounds of explosives was detonated by Timothy McVeigh in front of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma. There were 168 people murdered, including 19 children. Today the site is the Oklahoma City National Memorial, one site within the National Park Service system.

1775: Battles of Lexington and Concord in Massachusetts began the Revolutionary War between the colonists and the British government that ruled the colonies. Library of Congress: At Lexington Green, the British were met by approximately 70 American Minute Men led by John Parker. At the North Bridge in Concord, the British were confronted again, this time by 300 to 400 armed colonists, and were forced to march back to Boston with the Americans firing on them all the way. By the end of the day, the colonists were singing "Yankee Doodle" and the American Revolution had begun.