Seattle needs to sit down and watch this documentary.

It was made by Frederick Wiseman, and it concerns a dense and multicultural neighborhood in Queens called Jackson Heights where an estimated 167 languages are spoken and the streets are packed with a mind-blowing diversity of small businesses. But the future is not looking good for many of the working- and middle-class inhabitants of this urban paradise. The trouble began with Manhattan. It became super-expensive during the 1990s, and as a consequence, Brooklyn became super-expensive in the 2000s. Because Brooklyn is now "out of reach" for many people with good credit and stable incomes, real-estate investors are eyeing nearby affordable neighborhoods in places like Queens. And what makes Jackson Heights particularly desirable is the 7 train, which runs over Roosevelt Avenue.

The virtues of this elevated line, which is the leading visual image of the three-hour documentary, will prove to be the neighborhood's undoing. It can carry passengers from Jackson Heights to Manhattan in just 20 or 30 minutes. That means if you happen to work in Manhattan but can't afford to live there ("A hole goes for $2,500"), or in Brooklyn, then you might consider moving to this part of town, where you can get a one-bedroom apartment for just $1,600. This price is nothing for "gringos," says a middle-aged Spanish-speaking man during a meeting of business owners in a mall that's going to be torn down and replaced, rumor has it, by a Home Depot or some other kind of big business.

It is now only a matter of time before the neighborhood gets improvements, gringos move in, rents go up, and Jackson Heights, too, becomes "out of reach." Nothing it seems has the power to stop this process, which the great British-German sociologist Ruth Glass first called "gentrification" in 1964. The reason it happened in her time and place (London) is the same reason it happens today in NYC and Seattle: municipal inaction. If the real-estate market operates on its own terms with no checks or interruptions, then class differences will be expressed in spatial terms. It's not a mystery. It is as simple as that.

"We live in a capitalist society," says business owner Don Tobon at the beginning of the meeting in the doomed mall. "This is a country where private property is the most important thing. The landlord has all the rights. The right to raise the rent as high as he wants." The 50 businesses, some of which have been operating for nearly a quarter of a century and helped make their neighborhood vibrant, have to leave. Another business owner asks about the courts. Can something be done there? He is told that a lawsuit against the landlord of real-estate investors would be more expensive than just leaving the mall. "And it would be tiring to fight every day knowing in the end you will be kicked out," says Tobon, who is not a gloomy person in manner but is just being realistic. There is nothing they can do. Their neighborhood will be gentrified.

Wiseman's film turns out to be a document of a world entering its last days. The rich mix of cultures he meticulously and even impersonally captures (the South Asian restaurants, the Central American shops, the temples, the Islamic centers, the community meetings, the colorful parades, the many, many languages) will become a thing of the past. Everyone knows that it's only a matter of time before the gringos show up in large numbers. And these gringos have no real choice in the matter; they are under a lot of pressure to move outward. Yes, they may have more money than the average resident of Jackson Heights, but they also have been priced out of neighborhoods like Williamsburg and Long Island City. This is not directly their fault—this is out of their control. This is simply how market forces work in the absence of any legislative checks.

"Once this process of 'gentrification' starts in a district, it goes on rapidly until all or most of the original working-class occupiers are displaced, and the whole social character of the district is changed," wrote Ruth Glass. And what started this process in the first place? In London, it was a series of pro-market revisions to a 1947 planning act that, in the spirit of postwar Keynesianism, was more favorable to public enterprise than private enterprise—charges to developers that benefited the public purse, democratically managed development rights, and stabilized land values. By 1973, Glass wrote, inner London was well on its way to being "almost exclusively reserved for selected higher-class strata." What happened to inner London in the 1970s happened to Manhattan in the 1990s, and is now happening to inner Seattle today.

In Jackson Heights covers other conflicts, such as the members of the LBGT community protesting a business that will not serve transgender patrons, or a rally by a grassroots group that is fighting to make the neighborhood's streets safer for pedestrians. But these conflicts can be resolved. At present, however, Jackson Heights, like all urban neighborhoods in the United States, does not have the legislative power to resolve or challenge gentrification. Remember that it took a whole world war for London to establish a pro-public urban planning act. You have to wonder how bad it's going to have to get in Seattle before someone does something about it.