How do you quell a riot?

Missouri officials and commentators across America have asked that question many times in the wake of the violence plaguing Ferguson, Mo., which began after police killed an unarmed black teenager.

The answer is in an important but largely ignored document, written after the 1967 Detroit riots, that provides a thoughtful playbook for stemming urban unrest.

Detroit bore similarities to Ferguson. On a summer night in 1967, white police raided an unlicensed speak-easy frequented by African-Americans. A crowd gathered and fighting escalated. In the days that followed, fires and looters racked the city. Reports of snipers shooting police and firefighters shocked the nation. The Michigan National Guard was called out, but the situation only worsened.

The riots were ultimately controlled when President Lyndon Johnson sent in federal troops at the request of Michigan Gov. George Romney. Leading the federal response was Cyrus Vance, a former assistant secretary of defense and a future secretary of state.

Afterward, Vance wrote a report on the incident. One section, "Lessons Learned," is particularly relevant today. Mayors and governors should study his observations so that, for the next Ferguson, they will be better prepared.

One key problem in Detroit and in Ferguson was the poor quality of local law enforcement, ill-trained to handle a large riot. From Ferguson come videos of news crews being attacked with tear gas, images of combat-equipped police brandishing automatic weapons and disturbing accounts of excessive force.

During the 1967 Detroit riots, these problems were even graver: The local police and the Michigan National Guard shot at the slightest provocation. Only the deployment of better-trained federal troops brought calm.

On a human level, it is easy to understand why local law enforcement responds excessively in these situations. The police are scared. In a hostile urban area, it takes tremendous self-discipline to eschew protective armor and lethal gear. Local police do not have the level of training to know when not to use military-style equipment and how to use that equipment properly.

In Ferguson, Missouri Gov. Jay Nixon waited almost a week to replace local county police with the state police. After abating initially, however, the violence continued. On Monday, Nixon announced deployment of the National Guard. Had the governor not waited so long to make either of those decisions, it is possible the riots could have been calmed earlier by better trained personnel.

In 1967, Vance came to the unsurprising conclusion that African-American personnel, present then only among the federal troops, helped to calm racial tensions. In Ferguson, the local police are largely white. Gov. Nixon deserves credit for appointing state police Capt. Ron Johnson, an African-American, to coordinate the state's response.

Vance also made a timeless observation about riots: "rumors are rampant and tend to grow as exhaustion sets in."

The rumors emanating from Ferguson are varied and alarming. Consider just one from last week: that the government established a fake website to recruit would-be-hackers looking to attack the local police department's website.

Rumors can only be dispelled with frequent press conferences by senior personnel and with an open attitude toward the media. Unfortunately, the response in Ferguson was originally less than forthcoming to journalists, some of whom were arrested and intimidated.

A final lesson from Vance's report is the importance of a unified command — during and after a riot. A single person must be in charge of everyone, including all federal, state and local personnel. Only a unified command can respond in a swift and synchronized manner to the ever-changing nature of a riot. It does not appear Capt. Johnson has those powers.

Every city and state official in America should read Vance's report: No one can predict when the next riot will come or where, but responding correctly and quickly will save lives and property.

Nathaniel Zelinsky, 23, formerly of New Haven, holds a master's of philosophy in history from the University of Cambridge, where he studies as a Paul Mellon Scholar at Clare College.

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