1529 — At the Second Diet of Speyer, a group of rulers and independent cities protests the reinstatement of the Edict of Worms, beginning the Protestant Reformation.
1775 — The American Revolutionary War begins with the battles of Lexington and Concord.
1919 — Leslie Irvin makes the first successful voluntary free-fall parachute jump using a new kind of self-contained parachute.
1961 — The Bay of Pigs invasion of Cuba ends in success for the defenders.
1971 — Charles Manson is sentenced to death for the Sharon Tate murders. (As far as I know, that was never carried out.)
1993 — The 51-day siege of the Branch Davidian building outside Waco (Texas) ends when a fire breaks out. Eighty-one people die.
1995 — The Alfred P. Murrah Federal Building in Oklahoma City is bombed, killing 168. (Timothy McVeigh has since been tried, convicted, and executed. See 1971 entry above for perspective.)
2005 – Cardinal Joseph Ratzinger is elected Pope Benedict XVI on the second day of the Papal conclave.
2010 — US Supreme Court justices seem to split sharply on whether a law school can deny recognition to a Christian student group because it won’t let gays join.