BELFAST — The history of Ireland could one day be divided into two eras: before the Brexit referendum, and after it.

Until Britain voted to leave the European Union, the idea that Northern Ireland would one day perform a Brexit of its own and leave the United Kingdom to join the rest of the island in a single united Ireland seemed at best a distant possibility.

Then came June 23, 2016.

“It was like night and day, it was like someone flicked on a light switch,” recalled David McCann, a lecturer in politics at Ulster University and deputy editor of the Slugger O’Toole political commentary website.

Today, a vote on reunification is looking increasingly probable — some would say inevitable. Support for unification is rising on both sides of the border, and politicians and activists are scrambling to prepare for an eventuality they say suddenly seems more imminent.

“Brexit and the changing demographics of Northern Ireland is going to see the end of it" — Mark Daly, a senator with the Irish opposition Fianna Fáil party

“The referendum is coming,” said Mark Daly, a senator with the Irish opposition Fianna Fáil party who has been studying the practicalities of holding a vote on the issue. “The history of Irish reunification is still to be written. But it is going to be written in the next 10 years.”

The island of Ireland will not stay divided much longer, he added: “Brexit and the changing demographics of Northern Ireland is going to see the end of it.”

Border troubles

Northern Ireland was literally designed to remain part of the U.K. The border was drawn in the 1920s to carve out six of nine counties of the ancient Irish province of Ulster, which between them contained a comfortable majority of people who wanted to stay British as the rest of the island broke away to form a self-governing state.

The requirement to create a unionist majority is part of the reason why the establishment of a hard border after Brexit would be such a logistical challenge. Rather than cutting west to east across the island, the 300-mile border curves around to exclude inconveniently nationalist Donegal on the northwest coast, creating a winding division that is longer than the entire length of the island north to south.

During the 30-year conflict that ended in 1998 with the Good Friday Agreement, locals had to queue to be searched by armed soldiers in order to visit the shops, go to work or to church across the border.

The creation of the European Union’s single market in 1993 eliminated the need for economic checks. Peace in Northern Ireland — between mostly Catholic nationalists who wanted an all-island Ireland and largely Protestant unionists who favored remaining part of Britain — brought down the military watchtowers and reopened the roads.

Joint membership of the U.K. and the Republic of Ireland in the EU was key to keeping Northern Ireland’s Irish-identifying population happy. It underpinned the peace agreement, which allowed citizens of Northern Ireland to choose British or Irish nationality, or both. The border disappeared — the only clue are the subtly different road signs — leaving those who oppose its existence largely free to ignore it.

Brexit flips that all on its head. A hard Brexit, with the U.K. outside the single market and the customs union, would cut through parishes, farms and backyards, raising economic barriers that haven’t existed for decades. Checks on goods and people would disrupt the lives of the tens of thousands of people who cross the border daily for work, study, to do their shopping, or even cross their own property.

The extent to which Brexit upset Northern Ireland’s political order can be seen in the result of two elections for the region’s governing assembly. In a vote held in May 2016, just before the Brexit referendum, the combined support for Sinn Féin and the Social Democratic and Labour Party — the region’s two largest nationalist parties — was at its lowest in 18 years.

“Obviously Brexit revealed a very disunited kingdom" — Graham Walker, professor at Queen’s University Belfast

Soon after the Brexit vote, the assembly collapsed in acrimony. The election that followed revealed a galvanized electorate: Sinn Féin swept to its best-ever result. And for the first time in the history of the province, unionist parties lost their majority in the assembly.

“For those who would argue in favor of the union, it’s making it more difficult for those arguments to be convincing,” said Graham Walker, a professor who works on Northern Ireland and Scotland at Queen’s University Belfast. “Obviously Brexit revealed a very disunited kingdom.”

East German precedent

Brexit shifted the debate in the Republic of Ireland too. Although there is broad support for unification south of the border, there was zero urgency about the issue before the British vote.

An aspiration toward peaceful unification is in the Irish constitution, and on principle all parties support it, but only Sinn Féin treated it as a live political issue. After the Brexit referendum, however, the border and Northern Ireland suddenly became vital issues of national concern.

This quickly translated into policy realities: In April 2017, then-Prime Minister Enda Kenny succeeded in securing the so-called East German precedent in the EU’s Brexit negotiation agreement. This spelled out that were Northern Ireland ever to vote to unify with Ireland, it would automatically be part of the EU without any need for an accession process.

It was a major boost to the pro-unification side in any future referendum, and it also re-normalized the concept. A united Ireland didn’t seem so fantastical when it was on the front page of the Financial Times.

The issue of a united Ireland then became an issue in the Fine Gael leadership election to replace Kenny. Leo Varadkar’s ultimately unsuccessful rival, Simon Coveney, called his policy proposition “Uniting Ireland.” He became deputy prime minister and foreign minister. It was a stark shift for a party that has always been seen as, on the spectrum of Irish political parties, perhaps the most comfortable with partition.

Varadkar has since vowed to stand up for northern nationalists, promising they would “never again be left behind by an Irish government” in a landmark speech in December. According to the Irish Independent, Fine Gael has been polling focus groups on whether the government should “move towards a United Ireland, if this made sense following a Brexit deal.”

Generational shifts

A path to Irish unification is provided for in the Good Friday Agreement, which states that the decision to hold a vote on the issue rests with the secretary of state for Northern Ireland, a minister in the British government in London, “if at any time it appears likely to him” that a majority favors a united Ireland.

The wording was designed to allow both sides to read into it what they wanted. For Irish nationalists, it created the possibility of eventual reunification. For unionists the requirement of a popular demand for rejoining Ireland was something they considered so unlikely as to be a confirmation of the region’s place in the U.K.

“A lot of educated, outward-looking, liberal-minded unionists would tend to favor remaining in the European Union" — Dan O’Brien, economist

Particularly with the Tories in power in Westminster (or the “Conservative and Unionist” party to give them their full name), and reliant on the support of the Northern Irish Democratic Unionist Party for their majority, the idea of the secretary of state initiating a referendum may look remote to unionists.

But even before the Brexit vote, the island of Ireland has been undergoing several slow but powerful generational shifts. The first is demographic. Among Northern Ireland’s oldest residents, Protestants outnumber Catholics by two to one, reflecting how things were when the province was first drawn on the map. Among those of working age and younger, however, there is a Catholic majority.

The 2011 census showed a Protestant population of 48 percent versus a Catholic population of 45 percent, and some have predicted a Catholic majority in Northern Ireland by as soon as 2021. (Religion does not map perfectly onto political beliefs in Northern Ireland, but it is a good predictor, and the two communities use “Catholic” and “Protestant” as shorthand for each other.)

The second shift is cultural. Once, Northern Ireland was the more progressive of the two polities; its residents had access to divorce and contraception — both unavailable in an Ireland under the tight grip of the Catholic Church. Now, it is Northern Ireland that looks like a conservative outlier, after the Republic of Ireland voted to legalize gay marriage and abortion by large popular mandates. (Both remain illegal north of the border).

“A lot of educated, outward-looking, liberal-minded unionists would tend to favor remaining in the European Union,” said Dan O’Brien, chief economist of the Institute of International and European Affairs. “There are a chunk of unionists reconsidering [their options] in the context of Brexit.”

Similarly, Northern Ireland was once the wealthiest and most industrialized part of the island. Today, its GDP per capita is less than half that of the south and east, according to Eurostat. The United Kingdom once looked like the economically sensible option, compared to the reckless romance of nationalism; with Brexit, now it is British politicians putting ideology above prudence.

“Nationalism always had a big deficit around economic issues. Now with Brexit, a lot of business people — and that’s one thing that has shocked me with the people I deal with — now query whether remaining in the U.K. is the sensible option,” said McCann, the lecturer at Ulster University.

Policy vacuum

Polls differ wildly on the level of overall support for unification in Northern Ireland. Two June polls showed support for staying in the U.K. with a narrow lead over backing for a united Ireland: A LucidTalk poll had it at 45 percent to 42 percent; a survey by Lord Ashcroft polls put it at 49 percent to 44 percent. But a Queen's University Belfast survey showed support for unification at half that.

Yet the surveys are consistent in showing that Brexit, particularly a hard Brexit, eats into support in Northern Ireland remaining part of the U.K. In particular, it demolishes support among Catholics — who voted against Brexit by an estimated 85 percent and whose acquiescence to the status quo had until now secured Northern Ireland’s place in the U.K.

A majority of people in Northern Ireland now expect a referendum to occur within the next 10 years, according to the Lord Ashcroft poll. “I didn’t think there would ever be a border poll in my lifetime before Brexit, but I genuinely think now there will be,” said Jolene, a 29-year-old Belfast social work student, who said she would vote for a united Ireland. “I think it’s changed conversations in that people are now talking openly about a border poll,” she added. “I do think it will be inevitable.”

"You only have a referendum at the end of a long, long process where you debate all the issues” — Mark Daly

Among those who agree with her is Mark Daly, the Irish senator. A member of the Irish parliament’s Joint Committee on the Implementation of the Good Friday Agreement, Daly spent 10 months after the Brexit referendum gathering all available material on the practical steps to a referendum and unification: the economic implications, impediments, uncertainties, and how it could be achieved in law.

The result was “Brexit and the future of Ireland: uniting Ireland and its people in peace and prosperity” a weighty report of over 1,000 pages that is Ireland’s first parliamentary report on unification — a direct result of Brexit.

Daly’s quest revealed a vacuum of concrete policy on how a referendum could occur. There is no consensus on what a united Ireland would look like: whether the capital would be Dublin, whether the Northern Ireland assembly would continue as a regional parliament, what would be its flag and its anthem.

Even the criteria for holding a vote remain vague. How is the U.K.’s secretary of state for Northern Ireland to determine that a majority for unification “appears likely”? Is “a majority” 50 percent plus one, as had been widely assumed, or something more, as some politicians now argue? How can the two health care and tax systems be reconciled? How can the large financial subsidy Northern Ireland receives from London be replaced?

Daly fears that the British, Irish and Northern Irish administrations have all neglected to make a policy on any eventual unification, and could be caught unprepared if events take a sudden shift. “Policy neglect seldom goes unpunished,” he said.

“The lesson of Brexit is this: You do not have a referendum and then tell everybody what the future looks like. You only have a referendum at the end of a long, long process where you debate all the issues.”

Off a cliff

Daly has an unlikely ally on the other side of the border. Growing up on the streets of unionist north Belfast, Raymond McCord was known as a fighter. He has been a crusader ever since the death of his son, Raymond Jr, who was brutally beaten to death in 1997 at the age of 22 by loyalist paramilitaries from his own community.

McCord expects he would vote against a united Ireland in any referendum, because he hasn’t heard any convincing case about why he would be better off in the republic. “It’s just like Brexit,” McCord said. “‘Let’s vote for a united Ireland.’ But we don’t know what kind of united Ireland we’d have. The health service, housing, schooling, education. All these things need to be explained before any sort of poll could be done.”

McCord, a former welder and bouncer, describes himself as a working-class unionist. But he’s a strong believer in cross-community cooperation and believes that spelling out the conditions needed for a border poll will reduce acrimony in Northern Irish politics by stopping the main parties from using the issue to rile up their electorates.

His current battle is to force the British and Irish governments to clearly spell out the path to a united Ireland. He has begun judicial review proceedings in both Belfast and Dublin, arguing that the lack of clarity from both governments goes against the Good Friday Agreement.

“We’ve got to prepare, and we’ve got to prepare now. Events take over, and politicians forget this" — Mark Daly

“You can’t have a border poll called on the whim of a secretary of state who doesn’t live here,” he said. “It doesn’t affect them and they don’t really care.”

Whether a referendum could come quickly may be decided in the next few months, and it may be decided in Brussels.

If Britain reaches a deal with the EU that replicates Northern Ireland’s current status as part of the bloc, it would likely quell talk of a border poll. It would make the status quo look once again like the less risky option.

But if Britain and the EU fail to come to a deal the opposite could occur. Any moves to erect a border would inflame the issue, and an economic downturn could puncture the arguments of those who insist staying in the United Kingdom is in Northern Ireland’s best interests.

“If it goes off a cliff, if the Brexiteers get their way and they just run out the door, and there’ll be no customs union and no single market, and the border comes back, the reunification argument could accelerate,” said Daly. “It mightn’t be within eight years, it might be in five, it might be in three.”

“We’ve got to prepare, and we’ve got to prepare now,” he added. “Events take over, and politicians forget this.”