Plenty of factors can explain the crisis of housing affordability plaguing U.S. cities—a shortage of new construction, a lack of tenant protection, greedy developers and speculators, or a lack of upzoning. But according to San Francisco-based housing activist Randy Shaw, author of Generation Priced Out: Who Gets to Live in the New Urban America, one of the true challenges is the entrenched power and privilege of an older generation of homeowners.

“No progressive city posts “Priced Out: Only the Affluent Allowed” signs in it neighborhoods,” he writes in the book’s introduction.“But that’s what’s happened.”

Shaw, who runs the Tenderloin Housing Clinic in San Francisco, has a first-hand understanding of the causes of today’s crisis, having witnessed his city’s transformation over the last few decades into a poster child for extreme housing costs. He also knows many of the traditional solutions, having pushed for the tenant protections that make San Francisco a progressive beacon for renter’s rights.

But as he bounces from city to city in the book, showing how similar problems have manifested themselves in Austin, Los Angeles, Seattle, Denver, and elsewhere, it’s clear there’s a generational battle being fought. The entrenched power of homeowners to restrict the housing supply, even as the nation sees more expensive housing and increased wealth segregation across the country, shocked even a seasoned San Francisco activist.

“I sometimes feel akin to an emergency room physician as the victims of rising unaffordability and civil strife come to our office seeking help,” Shaw wrote, describing his experience in how home city. What shocked him, as someone who witnessed how that shift can change a city, is how widespread it has become.

A challenge so-called progressive cities aren’t meeting

Shaw says the housing crisis has taken on a different tone over the last few years because its impact is so widespread. What’s changed in many cities is how the middle class is being affected; now, low-income households and young adults aren’t the only ones facing long commutes or makeshift living situations due to a dearth of accessible and affordable options near jobs.

“If you’d spoken to me in 2011 and asked how Seattle is doing, I may have said it seems pretty affordable,” Shaw told Curbed. “Now, cities like Seattle, Portland, Minneapolis, and Austin all face similar problems as San Francisco. The nation perceived this as a problem that was only in certain cities, and now it’s spread.”

As soon as the housing market began recovering in earnest after the Great Recession, and prices really started rising in 2011 and 2012, says Shaw, cities that had restricted growth or favored single-family homes faced a reckoning. Generation Priced Out does a great job of telling the personal stories of families and tenants who can barely hang on; what’s even more damning is imaging all the other stories of those who missed opportunity because they couldn’t afford to move to big cities.

The fealty to policies that have restricted supply and raise prices challenge the self-image of many deep blue, Democratic cities; how can you be progressive and welcoming to all if low income, people of color, students, and the middle class can’t afford a place to live?

“So many cities are seeing long-standing pro-ownership policies come face to face with growth,” he says. “It’s challenging their progressive cred. If you drive a Prius and recycle, yet don’t allow apartments to be built, and then force people to drive 50 miles each way to work and cause all that pollution, you can’t say ‘out of sight, out of mind.’”

Los Angeles as a cautionary tale

Shaw works in San Francisco, but he grew up in the Westside of Los Angeles, so his descriptions of how many sections of that city went from working class to unaffordable offer some additional personal and historical perspective.

Like San Francisco, the city’s downtown development boom, economic growth, and increased population all occurred without the city building much housing. During the recent boom, working-class neighborhoods like Boyle Heights and Highland Park were targeted by speculators, and working class renters, who lacked tenant and housing protections, found themselves pushed out.

Like many other cities profiled in the book, generations of bad policy caught up during the last decade’s downtown building boom. Between 1980 to 2010, Los Angeles’s population growth exceeded housing growth by 42 percent. When demand and prices suddenly shifted, a city ripe for affordability issues faced disaster.

What Shaw found most eye-opening during writing and research was the widespread, entrenched power of homeowner groups. Between neighborhood groups and councils that held power over zoning and land-use decisions and the spread of NIMBYism, these older groups have often controlled the dialogue around adding housing supply, all while reaping an oversized amount of the gains from rising land values. As author Mike Davis once wrote, this “Sunset Bolshevism,” the collective political power of homeowners, has proven itself to be California’s strongest social movement.

“The most surprising thing was how widespread these homeowner groups was,” Shaw says. “The most powerful voters are homeowner voters.

Shaw highlighted Venice, the once-Bohemian beach community in Los Angeles, as a prime example. From 1960 to 2010, as the LA metro area added two million housing units, Venice added virtually none. Venice actually lost 700 housing units between 2000 and 2015, and the population decreased. It’s created incredible homeowner value, as well as an acute affordability and homelessness crisis.

Cities can change the narrative

While so many cities lament a steady shift toward a San Francisco-style housing situation, Shaw says he’s seeing hope, especially at a local level. Cities such as Seattle and Denver, while far from solving the issue, have shown the benefits of pro-growth policies. Portland, San Francisco, and Austin have also passed housing bonds.

There have been flickers of hope at the national level lately. Senators including Kamala Harris, Cory Booker, and Elizabeth Warren have all issued housing policy platforms. Shaw agrees that housing has been a larger national issue than its been in decades. But the solution, he says, can be found at the local level today.

“There’s been a wakeup call around America,” he says. “This book is based on the idea that cities can make a change and make this work.”