In 1970, the Vietnam War appeared to be winding down — enough that then-President Richard Nixon had even campaigned on a promise to end the unpopular conflict. However, in April of that year, U.S. troops under Nixon invaded Cambodia, escalating the war rather than winding it down, and sparking renewed protests across the country.

Things were particularly tense in the Northern Ohio town of Kent, the home of Kent State University. Protests in the town turned violent, with an angry mob throwing beer bottles at police, as well as the burning down of the university’s ROTC building, according to the Kent State University Library. (Per Far Out magazine, it is now thought that those responsible for the violence were not Kent State students.) Ohio’s governor at the time, Jim Rhodes, called the protestors “un-American,” and promised to “eradicate the problem.” Soon enough, the National Guard was called in.

On May 4, 1970, around 2,000 student protestors gathered at the university’s commons area, with National Guardsmen opposite them. The exact sequence of events that happened next is complicated, but long story short, the protestors purportedly threw rocks at the Guardsmen. In turn, the armed officers first deployed tear gas before opening fire, shooting an estimated 67 rounds in 13 seconds into the crowd. When the dust had settled, four students were dead, with nine others injured.