On May 4, 1970, 54 years ago today, members of the Ohio National Guard opened fire on a crowd of student protesters gathered on the campus of Ohio’s Kent State University, killing four students and injuring another nine. Several hundred students had been protesting against the Nixon administration’s expansion of the Vietnam War into Cambodia, and the mayor of the city of Kent asked the governor of Ohio to bring in members of the National Guard. News coverage of the shooting of unarmed protesters dominated headlines around the world and spurred hundreds of protests across the country. Gathered below are images from that pivotal day in American history.