Divorce is painful, especially when a marriage has lasted for more than 40 years and lives and finances are deeply intertwined. Emotions run high, assets are contested, and countless details need to be addressed. The June 2016 decision by the United Kingdom to leave the European Union has been no different: divorce negotiations have set off a heated debate about the United Kingdom’s future relationship with the European Union and strained arrangements with Northern Ireland and Scotland.

The British government has been an ambivalent member of the EU family from the beginning. In 1957, the United Kingdom opted out of early membership in the European Coal and Steel Community, reluctant to cede sovereignty to a supranational institution and concerned about damaging ties to the Commonwealth. In 1973, the British government joined the European Economic Community. But over the years, it negotiated a rebate that reduced its financial contributions and opted out of several flagship policies, including the euro and the Schengen travel area.

When former Prime Minister David Cameron held a referendum on EU membership in June 2016, he was seeking to end a years-long argument within his Conservative Party over the United Kingdom’s place in Europe. Opinion polls showed the public did not identify Europe as their most important issue before he announced the referendum in early 2016. Following a contentious campaign, British voters opted by a 51.9 to 48.1 percent margin to leave the EU. Attitudes varied across the country, with solid majorities in Scotland, Northern Ireland, and London preferring to remain.

On March 29, 2017, the British government notified the EU of its intent to withdraw by invoking Article 50 of the EU’s Lisbon Treaty. In June 2017, the two sides began messy negotiations about the terms of the separation, which was scheduled to take effect on March 29, 2019. London conceded to Brussels’ preferred sequencing for the talks: finalizing the divorce before addressing the future. There was logic to this approach, as the European Union wanted the United Kingdom to make a clean break before determining new arrangements. In November 2018, the United Kingdom and the European Union negotiated a legally binding withdrawal agreement that established the terms of departure, as well as a non–legally binding political declaration that set forth guiding principles for the future relationship. The British Parliament has struggled to ratify these documents amid arguments about the preferred nature of the United Kingdom’s relationship with Europe, largely along the same lines as the debates that precipitated the referendum.

Greater divergence from EU regulations will afford the United Kingdom more economic and trade independence, but at the cost of more intrusive checks on goods crossing the Northern Ireland border.

The backstop for Northern Ireland has become a proxy for this feud. The United Kingdom is currently part of the European Union’s customs union and single market. It will leave both after Brexit, which will raise the status of the Irish border to a customs border with associated controls. This would be pragmatically cumbersome and psychologically devastating for many who live in Northern Ireland, given the history of violent conflict and recent success in removing military watchtowers and checkpoints on the border as part of the peace process.

Both the United Kingdom and the European Union want to avoid the imposition of a hard border, ideally by addressing the matter through their post-Brexit economic relationship. Unless and until such arrangements are made, however, the European Union has insisted on a backstop provision in the withdrawal agreement: the entire United Kingdom will remain in a customs union with the European Union, plus Northern Ireland will comply with additional single-market regulations on goods and food.

An uncomfortable reality has become impossible to ignore: greater divergence from EU regulations will afford the United Kingdom more economic and trade independence, but at the cost of more intrusive checks on goods crossing the Northern Ireland border. The negotiating aims of British Prime Minister Theresa May—leaving the EU single market and customs union, preventing a hard border with Ireland, and ensuring a countrywide approach to Brexit—created a “trilemma” that has proven impossible to reconcile. Brexiteers in her party fear the United Kingdom could remain trapped in the customs union, as the backstop is not time limited, nor does it allow for unilateral withdrawal. Northern Ireland’s hard-line Democratic Unionist Party (DUP), whose ten parliamentarians have propped up May’s conservative government since she lost her majority in the June 2017 snap elections, does not want the region to be treated differently from the rest of the United Kingdom. The Labour Party has advocated for a softer Brexit that keeps the United Kingdom in the customs union, while some Labour members along with Liberal Democrats and Scottish Nationalists oppose Brexit entirely. Yet May, motivated by a desire to preserve Conservative Party unity, has repeatedly sought to change the backstop (something the European Union opposes) rather than amend the political declaration by allowing more alignment in the future relationship (which the EU would facilitate).


Just as divorce can be hard on children, Brexit has created challenges for the constituent parts of the United Kingdom, particularly Northern Ireland and Scotland. Northern Ireland consists of six counties that remained a part of the United Kingdom after Ireland gained independence in 1921. The Protestant and predominantly unionist community, and the Catholic and largely nationalist one, continued to contest the status of this territory long after that split. Decades of violence, known as the Troubles, left more than 3,600 people dead in the late twentieth century. The conflict ended with the 1998 Good Friday Agreement, which created a power-sharing arrangement that gave both communities a say in regional governance. Paramilitary groups decommissioned their weapons and the British government reduced its military presence. The EU membership of both the United Kingdom and Ireland enabled an open border, which supported the fragile peace in Northern Ireland by removing additional physical, economic, and psychological divisions between the two countries.  

In the Brexit referendum, 55.8 percent of voters in Northern Ireland preferred to remain in the European Union. Several weeks after the vote, the first minister and deputy first minister of Northern Ireland—who represented different communities and held opposing positions on the referendum—sent a joint letter to May stating their shared concerns about the consequences of withdrawal for the region. (The DUP leader had supported Brexit but still wanted to ensure free movement of people and goods across the border, continued EU funding to support economic development and peace initiatives, and protection of the agrifood sector from tariff barriers.) The power-sharing executive collapsed six months later amid a local scandal, with politicized Brexit debates hindering efforts to reconstitute it. January 2019 marked two years with no government in Northern Ireland.

Northern Ireland’s postconflict society—where “peace walls” divide communities, only seven percent of children attend integrated schools, and dissident paramilitary groups still detonate car bombs—has grown more polarized as Westminster squabbles. A December 2018 poll found that 69 percent of unionists oppose Northern Ireland leaving the EU under terms that are different from those of the rest of the United Kingdom; in contrast, 88 percent of nationalists and 65 percent of overall respondents see this scenario as advantageous. Similarly, two-thirds of unionists would rather the United Kingdom leave the European Union with no deal (even if that required border checks) than remain; 90 percent of nationalists prefer to stay in the EU under those terms. Notably, a poll conducted in March 2019 found that both communities (over 60 percent on each side) would support a softer exit for the entire United Kingdom if it leaves the EU.

Northern Ireland’s postconflict society has grown more polarized as Westminster squabbles.

Brexit has also raised questions about the future status of Scotland, whose ties to England date to the union of the crowns in 1603 and parliaments in 1707. The Scottish Parliament was established in 1999 as part of Prime Minister Tony Blair’s effort to devolve power across the United Kingdom. The government, which has been led by the Scottish National Party since 2011, held a referendum in September 2014 on whether Scotland should become an independent country. With turnout over 84 percent, Scots voted by a 55.3 to 44.7 percent margin to remain in the United Kingdom.

In the Brexit referendum two years later, 62 percent of voters in Scotland (including majorities in all districts) preferred to remain in the EU. First Minister Nicola Sturgeon quickly called for a second independence referendum, citing the “significant and material change in circumstances” that her party’s election manifesto said could trigger demands for another vote. Despite initial enthusiasm, opinion polls have not shown a substantial increase in support for independence. For starters, Scots are tired of voting: from 2014 to 2017, they cast ballots in two referendums, two British elections, Scottish Parliament elections, and local elections. They have learned that referendums do not definitively resolve political issues. Messy Brexit negotiations have further dissuaded voters: if it takes this much wrangling to end a 40-year union, unraveling 300-year-old ties will be that much harder. The Northern Ireland debate has highlighted that an independent Scotland in the European Union would need a border with a post-Brexit England.


How, when, and even if the United Kingdom will leave the EU remains unclear. Assuming it does leave, the nature of its departure will shape its future relations with Europe. Protracted and contentious negotiations have already diminished trust between London and Brussels, damaged the United Kingdom’s reputation across the continent, and fueled the antipathy of Brexiteers at home. The goodwill between London and Dublin, nourished by decades of successful stewardship of the Northern Ireland peace process, is also dwindling.

If the United Kingdom departs with no deal, there will be no divorce agreement, no transition period, and no protection for the Irish border. The separation will be clean in the sense that none of the old constraints will apply. But it will also be chaotic, as the sides will be forced to develop piecemeal mechanisms for everything from customs and tariffs to citizens’ rights and intelligence sharing.

If there is a lengthy extension to its exit date, the United Kingdom must find a way out of the current impasse. Although British voters, journalists, and even the prime minister have heaped derision on a gridlocked Parliament, polarized legislators represent a divided country. A snap poll after the second defeat of May’s deal revealed public unhappiness with her deal as well as a rise in support for multiple conflicting positions: no deal, a second referendum, and remaining in the EU. If the United Kingdom is forced to elect representatives to the European Parliament in May as a condition of a longer extension, its electorate may well choose parliamentarians who reflect Brexiteer anger or hinder the EU’s budgetary debates and pending reforms.

Even if the United Kingdom eventually agrees to a deal finalizing the divorce, the sides must then begin the painstaking process of determining their future relationship. Twenty-one months have been budgeted for this process, but it could take much longer—particularly given the continued domestic squabbling. The United Kingdom will have limited negotiating leverage. But given how close it lies and how many interests it shares with Europe, the EU should continue to cooperate with its ex on matters of security as well as on economic, social, and political affairs. Married, divorced, or uncomfortably separated, the United Kingdom and the European Union will be tied to each other for years to come, after all.

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  • AMANDA SLOAT is Robert Bosch Senior Fellow in the Center on the United States and Europe at the Brookings Institution.
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