A bomb thrown at police breaking up a peaceful eight-hour-day rally in Chicago's Haymarket Square killed seven officers; police gunfire killed at least four workers. Eight anarchists were convicted for their politics rather than the bombing — four were hanged, one died in his cell — in the case that gave the world May Day.

On May 4, 1961 the original 13 Freedom Riders — seven Black and six white civil-rights activists organized by the Congress of Racial Equality (CORE) — departed Washington, D.C. on two Greyhound and Trailways buses bound for New Orleans. The interracial group rode together in defiance of Jim Crow segregation at southern bus terminals and on interstate transportation, testing the U.S. Supreme Court's recent Boynton v. Virginia (1960) ruling that segregation in interstate travel facilities was unconstitutional. The Riders faced mob violence in Anniston (May 14, where one bus was firebombed), Birmingham, and Montgomery, drew federal intervention from Attorney General Robert F. Kennedy, and were arrested en masse in Jackson, Mississippi. Hundreds of additional Riders followed through the summer; the campaign forced the Interstate Commerce Commission to issue an enforceable desegregation order in September 1961.

The Kent State massacre took place when Ohio National Guard fired 67 rounds into a crowd of students protesting against the bombing of Cambodia, killing four and wounding nine others including bystanders.