So many things make America combustible right now: mass unemployment, a pandemic that’s laid bare murderous health and economic inequalities, teenagers with little to do, police violence, right-wingers itching for a second civil war and a president eager to pour gasoline on every fire. “I think we’re indeed in a moment where things are going to get a lot more tense before they get more peaceful,” said the University of Michigan historian Heather Ann Thompson, who won the Pulitzer Prize for her 2016 book “Blood in the Water: The Attica Prison Uprising of 1971 and Its Legacy.”…

These demonstrations were sparked by specific instances of police violence, but they also take place in a context of widespread health and economic devastation that’s been disproportionately borne by people of color, especially those who are poor. “Sociologists have studied collective behavior, urban unrest for decades, and I think it’s safe to say that the consensus view is that it’s never just about a precipitating incident that resulted in the unrest,” Darnell Hunt, dean of social sciences at U.C.L.A., told me. “It’s always a collection of factors that make the situation ripe for collective behavior, unrest and mobilization.”

Keith Ellison, Minnesota’s progressive attorney general, told me that lately, when he goes out walking or running in Minneapolis, he feels a “coiled sort of anxiousness ready to spring.” Many people, he said, “have been cooped up for two months, and so now they’re in a different space and a different place. They’re restless. Some of them have been unemployed, some of them don’t have rent money, and they’re angry, they’re frustrated.”