Every night in November 1968, National Guardsmen circled the streets in Wilmington, Delaware, armed with loaded rifles and ready to put down racial violence in the city’s most impoverished neighborhoods. Every so often, they’d stop to hassle Black residents, using racial slurs to refer to the people they’d been sent to the city to subdue.

Their job was to stop riots and looting from breaking out after the assassination of Martin Luther King Jr.—an event that had taken place seven months earlier. Though the city’s Black residents had rioted briefly after King’s murder and the mayor had requested a National Guard presence, the city was now at peace. Nonetheless, Delaware’s governor, Charles Terry, was convinced its Black residents would use any chance they could get to instigate more violence, and asked the National Guard to stay.

Lasting a full year, the occupation of Wilmington was the longest military occupation of an American city in history—and the most extreme response to riots that broke out in over 100 American cities after King’s murder on April 4, 1968. It only concluded with the election of a new governor in January 1969.

News that James Earl Ray had gunned down Martin Luther King Jr. on a Memphis balcony hit the United States like a thunderbolt. King had been in Tennessee to support striking sanitation workers as part of his Poor People’s Campaign, and just the day before the assassination had delivered a rousing speech in which he said he wasn’t afraid of death.

King also told listeners that they could achieve social change without violence. “We don’t have to argue with anybody,” King said. “We don’t have to curse and go around acting bad with our words. We don’t need any bricks and bottles. We don’t need any Molotov cocktails.”

His words were pointed: King was under fire by members of the Black Power Movement who argued that nonviolent resistance was ineffective, and just the summer before, urban riots in Detroit and nearly 160 other cities had caused widespread destruction. Yet in response to King’s murder, expressions of grief and anger—including civil unrest and destruction of property—erupted around the country.

Though the riots were incited by King’s death, they had other causes. Segregation had been outlawed, but discriminatory housing policies, white flight to the suburbs, and income disparities pushed many Black urban residents into largely African American, low-income areas. These areas were often poorly maintained, and African Americans there were hassled by local police and underemployed.

Just a month before King’s death, officials in the tri-state area predicted that the same things that had made people riot in the summer of 1967 would precipitate new riots in 1968. “The approach of summer finds conditions as explosive as ever,” wrote The New York Times. Those conditions included unemployment, a lack of suitable housing and widespread discontentment over policing and schooling.

For many, King had represented the promise of a better life for African-Americans. But with his death, that hope seemed to have died, too. Black leaders like Floyd McKissick, director of the Congress of Racial Equality, tried to come to terms with King’s death and its meaning for the broader civil rights movement.

“Nonviolence is a dead philosophy and it was not the Black people that killed it,” he told a reporter from the New York Times the night of the assassination. “It was the white people that killed nonviolence and white racists at that.”

By then, though, King’s death had already helped spark the tinderbox of African American grievances in urban settings. As word of King’s murder rang through the streets of cities like Washington and Baltimore, people began to gather in public areas. Some sang songs and marched; other people’s mourning turned violent.

“People were out of control with anger and sadness and frustration,” Virginia Ali, who owned a chili restaurant in Washington, D.C., told Washingtonian in 2008. Rioters—many of them teenagers—began burning businesses and looting.

Starting April 4, civil disturbances broke out in places like Los Angeles, Trenton, New Jersey, Baltimore, and Chicago. Many cities had been taken aback by the violence of the “long, hot summer” of 1967, in which nearly 160 riots broke out nationwide and Detroit became a war zone during five days of rioting. In response, city officials had spent a year preparing for more unrest. So had the military, and as soon as riots broke out the U.S. Army began to mobilize using plans they’d developed in 1967.

President Lyndon B. Johnson was worried that leaders would respond with unnecessary force. After meeting with Black leaders in his office the night of the assassination, he contacted governors and mayors to ask them not to respond with too much force. Privately, though, Smithsonian notes, he bemoaned their reactions. “I’m not getting through,” Johnson told aides. “They’re all holing up like generals in a dugout getting ready to watch a war.”

Though Johnson spoke on national television asking the public to deny violence a victory, riots had already begun. Then, cities and states began to crack down. In Cincinnati, a curfew was established and 1,500 National Guardsmen flooded city streets. In Pittsburgh and Detroit, even more National Guard members headed in. In places like Baltimore, troops used bayonets and tear gas to keep protesters at bay. And in Washington, D.C., Johnson eventually sent in nearly 14,000 federal troops to subdue the violence.

Despite the unprecedented—and, in some viewers’ eyes, unwarranted—use of force, most cities were back to normal within weeks. Wilmington, however, was not. Though the city’s mayor asked the National Guard to leave after the violence subsided a week after King’s murder, Governor Terry ordered indefinite National Guard patrols that were widely regarded as ineffective and racist.

“The National Guard here has become a symbol of white suppression of the Black community,” city solicitor O. Francis Biondi told the New York Times in November 1968, seven months after the occupation began.

Some cities did sidestep the violence—Los Angeles used a coalition of police and social leaders to convince people not to riot, and in New York the city’s mayor, John Lindsay, kept riots at bay by begging citizens in Harlem not to succumb to violence. But though cities had different responses to King’s death, the nation continued to worry about what would come next for race relations in the United States.

“I don’t think young people understand the struggle during that time,” Ali told the Washingtonian. “I’m amazed we withstood it.”

America in Mourning After MLK's Shocking Assassination: Photos