Brexit has ripped apart the United Kingdom, warning us how nations may, through a series of political blunders, degrade themselves. America should worry.

Stable, commonsense Britain — never a fully accurate picture — could have stumbled on except for the 2016 referendum on leaving the European Union (Brexit) that unexpectedly passed. Granted, Britain had underlying problems, but Brexit broke British politics.

Now, as both Tories and Labour destroy themselves, a new party system is emerging, probably dysfunctional. Under Cameron and May, the Conservatives splintered over an unworkable Brexit, now entering a grim final act under new Tory Prime Minister Boris Johnson.

Labour under Jeremy Corbyn lurched leftward and backward, embracing Marxism and revolution. The medium-sized centrist Liberal Democrats, who oppose Brexit, are already growing. Nigel Farage’s new super-sovereignty Brexit Party will also gain in the next election, which could come later this year. Farage, the equivalent of Steve Bannon, toured the U.S. for Trump in 2016.

Two-party Britain looks set to fragment into a four-party system — weakened Tories and Labour, strengthened Lib Dems and Brexit Party — none winning much more than a quarter of the vote and rarely a majority of seats. This means, as already is sometimes the case, that smaller parties are needed to support minority cabinets. If that smaller partner withdraws over some policy dispute, the cabinet collapses. Bad for governing stability.

Scotland will vote for the Scottish Nationalists. Brexit pushes many Scots toward independence with continued EU membership. Greens, Scot Nats, Wales’s Plaid Cymru and Northern Ireland’s parties together will top a fifth of the vote. The United Kingdom is disuniting.

Another “hung Parliament” will require the (barely) largest party to seek support from smaller parties, which will attach demands. The Lib Dems will demand another Brexit referendum, something Tories reject. Labour might go for it, resurrecting the old “Lib-Lab” pact.

Britain, an EU member since 1973, prospered from free trade within Europe, but Prime Minister David Cameron in 2016 held a referendum on Brexit, supposing Remain would easily win, but Leave took 52 percent, a self-inflicted wound that hasn’t healed. Younger, pro-EU voters didn’t bother to vote, but older and rural voters who dislike immigrants did (sound familiar?).

Humiliated, Cameron resigned, leaving the mess to Theresa May. Britain then faced the alternative of a “hard” or “soft” Brexit. In the former, also called a “no-deal” Brexit, the United Kingdom crashes uncushioned out of the European Union. Some welcome it, but increasingly more fear it. May struggled for a smooth, soft Brexit that kept some cushions but her own divided party couldn’t approve one. Hard or soft, Brexit’s deadline is October 31, Halloween.

Boris Johnson, former mayor of London and foreign secretary, began as a newspaper columnist excoriating the EU with fabricated facts and quotes. He led the Brexit campaign, again mouthing untruths. Many call Johnson a hollow self-promoter. Most of May’s cabinet has fled. The twice-divorced father of five (or maybe six, four of them legitimate) moved into 10 Downing with his current girlfriend. Donald Trump and Johnson are often compared and praise each other.

Johnson says he would accept a hard Brexit but may have no choice; Commons rejected a soft one three times. “Leave means leave,” intone no-dealers. Brexit is supposed to unleash Britain from EU regulations and restore its former glory. Increased trade with the U.S. should more than offset losses in the Continental market (doubtful). Johnson counts on American connections and was actually born in New York; he gave up U.S. citizenship only in 2016 after a tax dispute. Will Britain get a transatlantic “special relationship”? Trump likes Brexit but demands trade advantages.

A soft Brexit would keep British trade with Europe tariff-free but without EU membership or worker mobility, a deal Norway negotiated. Cut off from its natural market, analysts fear, the British economy will suffer. Some banks and businesses are shifting operations and personnel out of Britain. Panic is setting in, and the pound is dropping.

The Northern Ireland problem, seemingly settled with the 1998 Good Friday Agreement, returns. Britain now must erect a “hard border” (sound familiar?) between a Northern Ireland that’s no longer in the EU and an Ireland that is, what they call the “backstop.” Free movement between the two sustained the fraying 1998 accord; a backstop weakens it. Leaving the Ulster part of the UK inside the EU won’t be allowed. The logical solution is to reunite Ulster with Eire, but Northern Irish Protestants oppose it. Post-Brexit economics may change some minds.

Britain’s plunge into self-isolation and weakness infects the U.S., namely, our cutting of long-standing trade and strategic partnerships. Our alliances have become conditional and unreliable. We have trade fights with many countries, none getting resolved. Even redone NAFTA could fail in Congress. Trump escalates China-U.S. trade tension by tariffing more Chinese imports, making world markets wobble. America’s abandonment of leadership has destabilizing consequences.