THE NOT-SO-UNITED KINGDOM: Will Britain's decision to leave the European Union cause the U.K. to break apart?

• Author: Smith, Patricia
• Position: INTERNATIONAL

In 2014, when the Scottish people voted in a referendum on whether to leave the United Kingdom, Adam Cubak wasn't at all sure that Scotland should be its own country.

That referendum failed. But since the U.K.'s vote to leave the European Union in 2016, known as "Brexit," Cubak has changed his mind.

"Brexit has made me want independence more," says Cubak, 21, a senior at the University of Glasgow. "Now I feel like Scottish independence is inevitable."

After four long years of negotiations between the United Kingdom and the European Union, Britain's exit from the E.U. is starting to take effect. But Brexit is having unintended ripple effects within the U.K. In Scotland, support for Scottish independence is growing. And in Northern Ireland, the Brexit deal has inflamed old tensions that date back more than a century.

This is causing many to ask whether Brexit might ultimately lead the United Kingdom--England, Scotland, Wales, and Northern Ireland (see map)--to break apart. "Brexit has not created new tensions, but it's unearthed and exacerbated existing tensions in both Scotland and Northern Ireland," says Amanda Sloat of the Brookings Institution, a think tank in Washington, D.C. "Brexit has the potential to be a turning point in both places."

Charles Kupchan of the Council on Foreign Relations is even more blunt: "It's completely conceivable that over the next decade or so, the United Kingdom will not hold together."

Signs of Trouble

In 2016, 52 percent of voters in the U.K. chose to leave the European Union, a federation of European countries that share free trade and open borders (see "What is Brexit?"). But support for leaving the E.U., which was formally established in 1993, was not uniform across the U.K.: In both Scotland and Northern Ireland, a majority of voters wanted to remain part of the E.U.

Brexit became official in January, and the final details on how trade and borders will be managed are still being worked out. But already there are signs of trouble in both Scotland and Northern Ireland.

In Scotland, Brexit has deepened support for independence, which has long been fueled by Scots' pride in their separate identity. After Scotland rejected breaking away from the U.K. in the 2014 referendum, most people thought the issue was settled. But that was before Britain voted to leave the European Union. Support for the E.U. is high in Scotland, and 62 percent of Scots opposed leaving the E.U. Many feel they are being forced to go...