The increase in segregation is citywide. The number of Minneapolis schools where fewer than one in 10 students is white has increased sevenfold since 2000. The number of high-poverty neighborhoods has tripled since that time. Now, 42 percent of the black population lives in majority-minority census tracts, up from 34 percent in 1990. Meanwhile, the percentage of affordable housing in higher-income white suburbs has declined to its lowest point since the 1970s, according to Orfield.

This is a strange fate to befall the first large city in the country to enact a fair-housing ordinance and one of the first states to pass a law outlawing housing discrimination based on race. And it’s one that is threatening the economic stability of Minneapolis, Orfield says. “Segregation has helped wrench apart the economic fabric of the region, as neighborhoods or even entire cities have found themselves crippled by the rapid, destabilizing increase in poverty,” he wrote in a 2015 report, “Why Are the Twin Cities So Segregated?”

So what happened? How could a city that was once so forward-thinking in both race and economics fall so fast?

First, it’s important to understand how the Twin Cities were, to better understand how their commitment to diversity might have morphed. Since the 1960s, the Twin Cities promoted equality between rich and poor cities by pooling public revenues. As my colleague Derek Thompson has written, part of the egalitarian nature of Minneapolis stems from when, in 1971, regional leaders came up with the Minnesota Miracle Plan, which required all municipalities in the Minneapolis-St. Paul area to contribute a large share of their growing commercial tax revenues back into a fund that would be invested back into the whole region. “By spreading the wealth to its poorest neighborhoods, the metro area provides more-equal services in low-income places, and keeps quality of life high just about everywhere,” Thompson wrote.

The region took a collaborative approach toward housing, too. The Metropolitan Council, which is the regional government, required through a Metropolitan Land Use Planning Act that all suburbs provide for their “fair share” of affordable housing. From 1970 to 1980, the percentage of cities in the region offering subsidized housing grew from 8 percent to 51 percent. Black residents living in census tracts where more than half of residents were nonwhite actually decreased from 45 percent in 1970 to 38 percent in 1980. Almost three-quarters of all new subsidized housing built in the Twin Cities between 1971 and 1979 was built in the suburbs, which was the best record in the nation, according to Orfield. By 1979, 40 percent of subsidized housing units were located in the suburbs, and low-income families could move to one of 97 different communities in the area.