Dawn breaks over London as votes are counted for the EU referendum.Toby Melville / Reuters

Among the uncertainties unleashed by the Brexit referendum, which early Friday morning heralded the United Kingdom’s coming breakup with the European Union, was what happens to the “union” of the United Kingdom itself. Ahead of the vote, marquee campaign themes included, on the “leave” side, the question of the U.K.’s sovereignty within the European Union—specifically its ability to control migration—and, on the “remain” side, the economic benefits of belonging to the world’s largest trading bloc, as well as the potentially catastrophic consequences of withdrawing from it. Many of the key arguments on either side concerned the contours of the U.K.-EU relationship, and quite sensibly so. “Should the United Kingdom remain a member of the European Union or leave the European Union?” was, after all, the precise question people were voting on.

But the referendum’s over, the question on the ballot is answered, and now there are new questions to resolve. One of them concerns the politics within the U.K., and how the United Kingdom as a unit will withstand the forces pulling its constituent parts not just away from the European Union, but from each other.

The United Kingdom’s four component nations went different ways in the referendum, with majorities in England and Wales wanting out and majorities in Scotland and Northern Ireland wanting in. With that divided outcome have come announcements from parties in both Scotland and Northern Ireland that each could re-evaluate its relationship to the others. In Scotland, Nicola Sturgeon of the Scottish National Party, which promoted and lost a Scottish independence referendum two years ago, announced that her party could seek a new one. In Northern Ireland, Martin McGuinness of the Irish nationalist Sinn Fein party—whose militant wing, the Irish Republican Army, fought a bloody decades-long battle to withdraw from the United Kingdom and unite with Ireland—has recommended a vote on independence from the U.K. and union with the Republic of Ireland.

The dynamics are different in each case. Though the nationalists lost Scotland’s 2014 independence referendum, a significant minority of 45 percent of Scots voted to leave the U.K.; meanwhile, Scots favored EU membership by a large margin in the Brexit referendum, with 62 percent voting in favor of staying. Would pro-EU sentiment be enough to push Scottish public opinion that last little bit in favor of independence? Would Scots be inclined to leap out of one union, the United Kingdom, for the sake of a different one, the EU? Polls taken prior to the referendum have suggested it’s not that simple—earlier this month, independence was not that much more appealing to Scots facing the prospect of Brexit than it was to Scots in 2014—and Scottish politicians have urged caution. Kezia Dugdale, the leader of the Scottish Labour Party, argued against a new referendum: “On the question of independence, many of the fundamental questions that were unresolved and unanswered in 2014, remain so,” she said. These include basic matters like what currency an independent Scotland would use (Scottish pounds? British pounds? Euros?). “What we don't need today is more turmoil, more upheaval and more economic chaos.”

On the other side of the Irish Sea, Northern Ireland will have the only land border between the United Kingdom and the European Union; it shares an island with the Republic of Ireland, an EU country, to the south. The implications of Brexit for this border, which has heretofore been open under EU freedom-of-movement rules, are not yet clear. But as Naomi O’Leary reported for The Atlantic earlier in the week, a stronger division of the Irish island is a potentially explosive issue—it’s one people in Northern Ireland fought over throughout the Troubles, the period of violence beginning in the late 1960s in which some 3,500 people were killed before the Good Friday Agreement, backed by the United States and Britain, stopped most of the fighting in 1998. As O’Leary noted: “The EU has pumped funding into projects to promote cohesion, and the region’s peace agreements are underpinned by EU law.”

But perhaps a more fundamental issue is that the open border between Ireland and Northern Ireland helped obviate an underlying cause of the conflict. Catholic nationalists had fought to unite Ireland’s north and south; Protestant unionists had fought to keep the north in the United Kingdom. Under EU arrangements, there was something for everybody; Ireland was “united” in certain ways, even while the U.K. exercised sovereignty over the north. But following the referendum—in which Northern Ireland voted to remain by a margin of 56 to 44 percentthe chairman of Sinn Fein declared that the British government had “forfeited any mandate to represent the interests of the people here in the north of Ireland in circumstances where the North is dragged out of Europe as a result of a vote to leave.” (The leader on the unionist side pronounced the outcome a “good result.”)

In the short term, a referendum on a united Ireland stands a much smaller chance of passing than a Scottish independence referendum, given Northern Ireland’s unionist majority. Yet as O’Leary wrote: “[A]ny move toward such a vote would face uproar from the unionist community, for whom even symbolic changes can be provocative. A 2012 decision to reduce the days on which the British Union Jack flag was flown from Belfast’s City Hall sparked weeks of protests and riots.” Nor does the Brexit referendum mean that the IRA and the Ulster Freedom Fighters will pick up arms again. But Northern Ireland’s peace is fragile, and its politics are polarized. And the dangers have apparently caught the attention of American policymakers. In acknowledging referendum outcome, President Obama specifically emphasized the U.S. commitment to “continued stability, security, and prosperity for Europe, Great Britain and Northern Ireland, and the world.”

There’s a certain irony in the image of celebrating Brexiteers waving the Union Jack to celebrate Britain’s coming withdrawal from the European Union. The flag is really an amalgam of flags, including the Scottish Cross of Saint Andrew, the English Cross of Saint George, and the Irish Cross of Saint Patrick. And the referendum outcome itself has raised the potential for the whole thing to unravel.

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