The Kent State Massacre in Ohio in 1970 where four protesting students were shot and killed by the US armed forces.
It was first recorded by Crosby, Stills, Nash & Young. David Crosby Stephen Stills Graham Nash Neil Young
Kent State massacre
The Kent State massacre
The song was written about the 1970 shootings during a non-violent peace rally at Kent State University in Ohio, where 4 people were killed by the National Guard.