In 1970, a demonstration against the Vietnam War and in favor of emergency aid to North Vietnam at Ohio State University's main campus in Columbus, Ohio swells to several thousand people. After several incidents in which demonstrators yell obscenities at campus and local police called in to "maintain order", Columbus's mayor Maynard E. Sensenbrenner calls for the assistance of the National Guard.

The following day, tensions at OSU-Columbus escalate when, just prior to the arrival of National Guard troops requested by Mayor Sensenbrenner, the campus Reserve Officer Training Corps erupts in flames. Attempts to put out the blaze are hampered by demonstrators, who throw rocks and bottles at police and firemen trying to extinguish it. When the Guard troops arrive, they set up headquarters on campus and make numerous arrests, employing tear gas and bayonets on the crowd. One student is injured by a bayonet.

Three days later, with demonstrators and National Guard troops still facing off on the OSU-Columbus campus, Guard troops read the assembled protesters a formal order to disperse or face arrest. When the protesters do not back down, the Guard troops advance on them. The student demonstrators retreat until they find themselves boxed in by a chain-link fence, at which point some of them begin moving forward, attempting to get out of the cul-de-sac. Several Guardsmen, apparently interpreting the students' forward motion as the start of an attack, fire their weapons into the crowd.

Chaos ensues. The crowd surges forward as the demonstrators, many of whom now fear they have been herded into a trap to be shot down en masse, try to break out. The opposing Guardsmen, none of whom have been trained in riot control, panic and begin firing indiscriminately. Eight students are killed and several dozen injured; of the slain, two are found to have simply been in the wrong place at the wrong time, rather than active participants in the protest. Two Guardsmen are also killed, one apparently by fire from another Guardsman's rifle, and several others are hurt.

The violence changes the political dynamic within the U.S. antiwar movement, escalating the importance of the Southeast Asian conflict, which until then had most often taken a back seat to the much closer war in Cuba.