On Aug. 28, 1964, African-Americans began three nights of rioting in Philadelphia. It was exactly a year after Martin Luther King, Jr. issued his iconic call for black freedom and equality at the March on Washington.

A half-century later we imprison disproportionate numbers of African-Americans, who are more likely to be targeted or killed by law enforcement officials. That’s what unleashed the recent riots in Ferguson, Missouri, following the police killing of Michael Brown — an unarmed black man — on Aug. 9.

That was also the most common trigger for the race riots of the 1960s, which sparked panic in the heart of white America. Between June 1963 and May 1968, our cities witnessed 239 riots involving over 200,000 participants. Eight thousand people were injured, and 190 lost their lives.

By August 1967, over half of white Americans told pollsters that they felt scared for their personal safety. Never mind that the vast majority of riot casualties were black. In the Watts riot of 1965 in Los Angeles, for example, 28 of 34 killed were African-American; in Newark’s 1967 riot, 24 of 26 dead were black.

Not surprisingly, the races differed in their analysis of the violence as well. In a 1967 survey, asking respondents to list causes of the riots, over two-thirds of blacks but just one-third of whites cited lack of jobs and decent housing for African-Americans. Half of blacks and less than 10 percent of whites mentioned police brutality.

Over the next 20 years, these numbers would help fuel a tectonic shift in American politics. Souring on the liberal social programs of the Great Society, millions of white Democrats deserted the party. They found a ready home in a revamped GOP and its call for “law and order,” a none-too-subtle appeal to racial anxieties.

And they found an effective standard bearer in Ronald Reagan, who played up the Watts riots in his successful bid to unseat California Gov. Edmund “Pat” Brown — the current governor’s father — in 1966. By 1980, when Mr. Reagan swept into the White House, law and order had become the official GOP creed. It resurfaced in 1988, when George H.W. Bush used the figure of Willie Horton — a black rapist paroled by Massachusetts’ Michael Dukakis — to win the presidency.

Democrats tried to play catch-up, but mostly in vain...