FILE - In a May 4, 1970 file photo, Ohio National Guard moves in on rioting students at Kent State University in Kent, Ohio. Four persons were killed and eleven wounded when National Guardsmen opened fire. The U.S. Justice Department, citing "insurmountable legal and evidentiary barriers," won't reopen its investigation into the deadly 1970 shootings by Ohio National Guardsmen during a Vietnam War protest at Kent State University. Assistant Attorney General Thomas Perez discussed the obstacles in a letter to Alan Canfora, a wounded student who requested that the investigation be reopened. The Justice Department said Tuesday, April 24, 2012 it would not comment beyond the letter.  (AP Photo, File)
FILE - In a May 4, 1970 file photo, Ohio National Guard moves in on rioting students at Kent State University in Kent, Ohio. Four persons were killed and eleven wounded when National Guardsmen opened fire. The U.S. Justice Department, citing "insurmountable legal and evidentiary barriers," won't reopen its investigation into the deadly 1970 shootings by Ohio National Guardsmen during a Vietnam War protest at Kent State University. Assistant Attorney General Thomas Perez discussed the obstacles in a letter to Alan Canfora, a wounded student who requested that the investigation be reopened. The Justice Department said Tuesday, April 24, 2012 it would not comment beyond the letter. (AP Photo, File) Credit: ap

Historians of the American Revolution refer to the opening of the Battle of Concord on April 19, 1775, as the “shot heard round the world.” On Monday, we observe the 50th anniversary of a burst of gunfire — shots heard round the world — that begged a nation finally to come to terms with the war in Southeast Asia.

Richard Nixon had won election as president in 1968 in part because of his “secret plan” to end the war in Vietnam. The secret plan, it turned out, was secret even to his secretary of defense, Melvin Laird, and to his secretary of state, William Rogers. On April 30, 1970, they learned along with the rest of the nation that Nixon had authorized the invasion of Cambodia, an officially neutral country on Vietnam’s western border. Just days earlier, in fact, Rogers had told Congress that “the administration has no intentions … to escalate the war. We recognize that if we escalate and get involved in Cambodia with our ground troops that our whole program is defeated.”

What happened? On April 25, two days after Rogers’ testimony before Congress, Nixon dined with his national security adviser, Henry Kissinger, and his friend Bebe Rebozo. Following dinner, Nixon watched the movie Patton for the sixth time. Kissinger later said about Nixon, “When he was pressed to the wall, his romantic streak surfaced and he would see himself as a beleaguered military commander in the tradition of Patton.”

Nixon made the decision to invade Cambodia the following day.

The sudden escalation of the war in Southeast Asia, which many Americans had been led to believe was winding down, triggered an avalanche of protests across the nation, especially on college campuses. The protests at Kent State University, in northeast Ohio, began May 1 in a park-like space at the center of campus called the Commons. Students gathered to hear several speakers denounce the war and Nixon specifically. In downtown Kent that night, students blocked traffic and lit bonfires in the streets, prompting the police to use tear gas and Kent’s mayor to seek assistance from the state’s governor, James A. Rhodes, who deployed the Ohio National Guard. The following day students set fire to the ROTC building on campus.

Conservatives viewed these student protests as despicable and destructive, the actions of privileged young people who were in college only to avoid the draft. Rhodes identified students as the “communist element” and pledged “to use every part of the law enforcement agencies of Ohio to drive” them out of the state. Spiro Agnew, Nixon’s vice president, verbally lacerated “the hardcore dissidents and the professional anarchists within the so-called peace movement.” Nixon himself referred to the protesters as “bums,” and Ronald Reagan, from his perch as governor of California, called for swift, retaliatory action against students. “If it takes a bloodbath, it takes a bloodbath,” Reagan said. “Let’s get it over with.”

The bloodbath began at 12:24 p.m. on Monday, May 4, 1970. Officials had tried to cancel the gathering scheduled on the Commons at noon that day, but students began arriving at 11, and approximately 3,000, most of them spectators, gathered by noon. Roughly 100 National Guardsman carrying M-1 rifles were stationed nearby.

The gathering began peacefully, but the Ohio National Guard general, using a bullhorn, ordered the protesters to disperse. They refused. A few students threw rocks at guardsmen. The Guard advanced with bayonets and tear gas and then began shooting.

In the space of only 13 seconds nearly 70 shots were fired, some into the air and others into the crowd of students. Four students were killed: Allison Krause, Jeffrey Miller, Sandra Scheuer and William Schroeder. The latter two were not protesters; they were bystanders. Nine others were injured. Schroeder, 390 feet from his killer, was shot in the back, as were two of those injured. Allison Krause, a first-year student in the honors college, was 330 feet — more than a football field — away from the guardsman who shot her.

News of the shooting, which some called the Kent State Massacre, reverberated around the nation and the world. Protests erupted on campuses across the country, including the University of Wisconsin and such unlikely venues as the University of Nebraska and the University of Arizona. In Seattle, protesters flooded Interstate 5, forcing it to close. On May 9, a week after the shooting, a crowd of 100,000 protested outside the White House. Nixon had brushed off the shootings with a dispassionate comment. “When dissent turns to violence,” he said, “it invites tragedy.”

The tragedy repeated itself a few days later when police fired into a dormitory at Jackson State University in Mississippi. Two African-American students were killed and 12 more wounded.

After reading the cover story of the Kent State shooting in Life magazine, Neil Young wrote the music and lyrics for Ohio, which included the famous opening line: “Tin soldiers and Nixon coming / We’re finally on our own.” Crosby, Stills, Nash & Young hurried into the recording studio, and Ohio hit the airwaves shortly thereafter, becoming one of the most famous protest songs of the Vietnam era. The Guardian described it 40 years later as “arguably the perfect protest song: moving, memorable and perfectly timed.”

Incredibly, 24 students and one faculty member, known as the Kent 25, were indicted on criminal charges later that year. None of the guardsmen was charged; the grand jury exonerated all of them, saying that they “fired their weapons in the honest and sincere belief … that they would suffer serious bodily injury had they not done so.”

Another study of the incident, released the following year, relied on both testimony from eyewitnesses and photographic evidence to conclude that between eight and 10 of the guardsmen had intended to shoot at the students, either to injure or kill. An audiotape discovered by one of the wounded students in 2007 allegedly captured the command to fire.

The Kent State shootings galvanized opposition to the war in Vietnam. I recall billboards depicting the event as a box score: “National Guard 4; Kent State 0.”

But Kent State also galvanized support for Nixon and the Vietnam War. In the wake of the tragedy of Kent State and the larger tragedy of the war itself, Nixon rallied his backers — the “silent majority,” as he called them — for support against the opponents of the war and against his political adversaries. He rolled to reelection in November 1972, and the fighting continued for several more years.

That’s something worth remembering half a century later.

Randall Balmer is the John Phillips Professor in Religion at Dartmouth College.