In a nocturnal video posted to his office’s YouTube channel, New York City Mayor Zohran Mamdani greeted this year’s April 15 tax day by announcing, “I said I was going to tax the rich. Well, today we’re taxing the rich.” Mamdani, who won the mayoralty by an absolute majority last November, recorded his video on Central Park South, one of the city’s poshest streets, in front of hedge-fund billionaire Ken Griffin’s apartment building as music that sounded vaguely like the soundtrack to HBO’s Succession played in the background. Mamdani chose the location with purpose: Griffin represents, to him, “the richest of the rich,” and therefore a source of revenue to fund his social programs via a “pied-à-terre tax.” The new levy will tax second homes owned in New York by non-residents valued at $5 million or more.

Griffin responded in a CNBC interview, saying he may reconsider a $6 billion construction project that would create an estimated 15,000 permanent jobs in New York and instead focus on future projects in Miami, where he resides. Quoted in the Wall Street Journal describing Mamdani’s video as “creepy and weird,” Griffin added that Mamdani’s singling him out “put me in harm’s way.” President Trump has weighed in, telling radio host Sid Rosenberg that any city’s mayor should “cherish” business leaders and “convince them not to leave” rather than drive them away.

According to the New York Post, Mamdani has reached out to Griffin to ease the tensions but received no response. If Mamdani needs more evidence that he might be in the wrong, however, he should look across the pond to the United Kingdom, whose Labour Party, in office since 2024, has raised taxes and abolished its so-called “non-domicile” (“non-dom”) tax exemption for the non-UK income of foreign nationals who reside in Britain. (Britain, like almost all countries except the United States, does not tax its own citizens’ foreign-earned income).

The results have been a disaster. According to figures cited by the Daily Telegraph, some 10,800 millionaires expatriated from the UK in 2024 alone, an average of one every 45 minutes. More jarring evidence came on May 15, just days after Griffin’s CNBC interview, when the Times of London released its 38^th annual “Rich List,” a compendium of the country’s richest 350 individuals, including UK citizens worldwide and foreign citizens residing in Britain.

For most of its history, the Times’s Rich List has been relatively stable, listing a familiar bevy of entrepreneurs, business executives, landowners, aristocrats, and others whose fortunes are tied to Britain. This year’s list, however, reveals what the Times calls “an exodus of wealthy individuals leaving the UK in the wake of tax changes.” According to the paper’s detailed analysis, at least 60 foreign nationals who appeared in 2024’s list—more than one in six—have been dropped, in almost all cases because they now reside in another country. Some left angrily. Eighty-two-year-old Norwegian-born shipping magnate John Fredriksen, who is a citizen of Cyprus, moved to the United Arab Emirates last year, telling Forbes that “Britain has gone to hell.” Christian Angermayer, a German-born entrepreneur, moved from the UK to Switzerland, telling Bloomberg that Labour’s tax hikes were a “huge mistake” and an “act of national self-harm.” Other departures have been quieter but highly visible. Indian billionaire Lakshmi Mittal, who had been on the list for decades and was named the richest man in Britain for eight consecutive years, disappeared from the list this year after moving to homes in Switzerland and Dubai. Mittal, ironically, was a major Labour Party donor.

The Times reckons that about one-third of UK citizens on the list, who still qualify for it due to their nationality, no longer live on British soil. Twenty-five people on the list now live in Monaco, while 19 live in the United States.

Signs indicate that the American left is simply not catching on, despite indications that well-to-do residents, like their British counterparts, are eagerly moving to less exacting tax jurisdictions. Affected Americans, however, can find meaningful tax relief by simply relocating to another state.

According to figures cited last August by the New York Post, New York City’s share of America’s millionaires declined by 31 percent between 2010 and 2022, years roughly coinciding with the mayoralties of Bill de Blasio and Eric Adams, both of which saw rising costs, tax increases, declining urban conditions, and significant outmigration during the COVID-19 pandemic. Despite his backpedaling on Griffin, Mamdani this week announced an ambitious housing plan that may seek to “transfer ownership” of residential real estate from private landlords to what he calls “responsible stewards,” including “community land trusts, nonprofits, or even the tenants themselves.” One can only wonder if Ken Griffin will stay long enough to see if his Central Park South residence becomes a Soviet-style communal apartment.

In April, Seattle mayor Katie Wilson suggested in a video broadcast on Fox News that analyses predicting capital flight from Washington state are “super overblown.” She offered a dismissive wave and callous “bye” to hypothetical high-income earners who would move elsewhere.

In November, California will hold a union-sponsored ballot initiative on a one-time “billionaire tax” that would impose a five-percent surcharge on the global assets of all California residents and trusts valued at $1 billion or more. Several individuals in that category have already reportedly moved, though only those who did so before Jan. 1, 2026, will escape the prospective tax liability due to a controversial retroactivity provision.

Fortune has documented six California billionaires who appear to have left in time, taking with them an estimated $27 billion in projected tax revenue—more than a quarter of the expected amount, possibly along with massive amounts of state investment and job creation. They include Google founders Larry Page and Sergey Brin and investment titan Peter Thiel, all of whom now live in Florida, whose state constitution bans income and inheritance taxes.

Florida, perhaps not coincidentally, is also by far the top U.S. state destination for British expatriates who relocate to America. According to Folio Weekly, a Jacksonville news source, the state is now home to nearly 60 percent of the Britons who reside in the United States. Florida is, in fact, so popular in the UK that BBC Channel 4 this month launched a 20-episode program called Escape to Florida, which chronicles what its website calls “the fun-filled lives of the growing number of British and Irish expats who are turning their backs on grey skies and rising living costs at home and seeking a fresh start in America’s Sunshine State.”

As for Britain, in what may be the world’s most poignant lesson in wealth migration, only one billionaire appears to have relocated to that country in the past year and landed on the Times’s Rich List: the American investment banker Warren Stephens, who took up residence in London in 2025 as the new U.S. ambassador to the United Kingdom. As a foreign diplomat, he is exempt from UK taxes.