SAN FRANCISCO — Cities throughout the Bay Area are perpetuating unconstitutional racial segregation with their housing laws, local author Richard Rothstein said Wednesday during a talk about his groundbreaking book, “The Color of Law.”

The book, which made waves when it hit shelves last year, lays out the history of housing policy in the United States and highlights the role racism and segregation played in shaping it. He spoke about the book, answered questions and signed copies at the Brava Theater Center in San Francisco for an enthusiastic crowd of more than 100 people who occasionally interrupted him to clap or cheer when he made a particularly striking point.

Rothstein, a UC Berkeley Haas Institute fellow, sought to blow up the notion that the segregation present in nearly every city in the Bay Area and beyond “just happened.” Cities were segregated on purpose through federal and local policies such as exclusionary zoning laws — which to this day prevent condos, apartments or even small single-family homes, which African Americans are more likely to live in, from infiltrating mostly white suburban neighborhoods in “many, many” Bay Area communities, he said.

“If you understand that the communities with these zoning ordinances were created in an unconstitutional fashion, then I don’t think it’s unreasonable to conclude that the zoning ordinances themselves are unconstitutional because they perpetuate a civil rights violation,” he said during the event organized by pro-development advocacy group Mission YIMBY.

Many neighborhoods in the Bay Area and across the country were segregated for the first time intentionally by the federal government, with the advent of public housing in the 1930s, Rothstein said. The public housing program, which started under the New Deal and then continued to house war workers during World War II, built separate projects for African Americans and whites. In Richmond, the government built housing for white shipyard workers and separate housing for black shipyard workers. In San Francisco, the government built four public housing projects for whites, and one for African Americans in the Western Addition (where the Fillmore District is now).

In the decades that followed, middle-class whites bought homes and flocked to developing suburbs that were closed to African Americans — such as Westlake in Daly City, Rothstein said. These developments, which were backed by the Federal Housing Administration, refused to sell, or allow homes to be resold or rented to African American families.

As a result, African Americans couldn’t buy homes and weren’t able to accumulate wealth through generations of home appreciation the way their white peers did. Today, black incomes are about 60 percent of white incomes on average, but black wealth is just 10 percent of white wealth, Rothstein said.

Rothstein’s words struck a chord with many in the audience. Omar Harris, who is African American and grew up in a poor, segregated neighborhood in Mississippi, said Rothstein’s book helped him make sense of his family’s experience in a way he hadn’t before.

“I lived in the worst part of the city. It was nothing that we did wrong — that’s what you have to understand,” said Harris, a 45-year-old veteran who lives in San Francisco and works in sales.

Liz Miller walked away from Wednesday’s talk feeling inspired to try to help change the region’s problematic policies. Miller, a 45-year-old HR consultant who lives in San Francisco, said reading the book opened her eyes to an uncomfortable new reality.

“I really never understood why things are the way they are,” she said. “And honestly, I think I was too afraid to ask the question.”

Sam Moss, executive director of affordable housing developer Mission Housing, said Rothstein’s work helped him comprehend the roots of the roadblocks he’s faced when trying to build housing in San Francisco.

“When I began as the executive director of Mission Housing, I naively assumed that we would be able to build the type of high-quality apartment buildings we build in the Mission everywhere, maybe even the Sunset,” Moss said as he introduced Rothstein before the event. “And I learned quickly that that was not even legal.”

Those exclusionary housing policies mean African American families, who often rent because they haven’t had the same opportunity for home ownership as whites, can’t move into white neighborhoods. This segregation has taken a toll on society, Rothstein said. It’s led to inequalities in schools, the criminal justice system, health care and job opportunities between blacks and whites, and even contributed to the political polarization of the county.

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“There’s nothing de facto about this,” he said. “This is a federal policy that’s as unconstitutional as the segregation of water fountains or pools or restaurants. And yet we’ve done nothing about it.”