While Kent State was not the only instance of violence against student protesters, it immediately became a byword for state-sanctioned violence. Campuses nationwide erupted in protest. Krause, Miller, Scheuer and Schroeder became martyrs, their deaths memorialized by the band Crosby, Stills, Nash and Young in their song “Ohio.” The tremors were felt all the way to the White House; according to H.R. Haldeman, Nixon’s chief of staff, they precipitated the sense of political paranoia within the administration that set Watergate in motion.

Thomas M. Grace, one of the students shot on May 4, went on to become a historian. Among his books is a well-received history of the protests, “Kent State: Death and Dissent in the Long Sixties.” In it, he argued that the shootings and the mass student strike had three immediate, tangible effects.

First, the ensuing political pressure propelled Nixon to end the unwarranted Cambodian invasion earlier than anticipated, on June 30, 1970. Second, the horror of students dying at the hands of a militaristic state helped propel Congress to pass the War Powers Act in 1973, which curbed the president’s war-making authority. Third, the protests contributed to the ratification of the 26th Amendment a year later, which lowered the voting age from 21 to 18. Legislators recognized, not only that young adults old enough to be drafted should have the right to vote, but the civic awareness necessary for voting was evident in the acute appreciation of political problems that young people poignantly showed during the spring of 1970.

Looking back, 50 years later, we can also see clear but less tangible effects. Along with cultural touchstones like the Manson family murders and the concert at Altamont, Kent State marked the symbolic end of the 1960s, stretching from the optimism of John F. Kennedy’s inauguration through the March on Washington to the long hot summers of riots, assassinations and radical activism. If, as the sociologist Todd Gitlin noted, the decade was marked by both hope and rage, then the events of May 4 brought the sober recognition that neither could overcome the will of a militaristic state and a conservative political backlash.