(Bloomberg) — Following an unexpected election triumph, Sinn Fein leader Mary Lou McDonald wasted little time in calling for a united Ireland, demanding a referendum on reunification within five years.Meanwhile, one of her successful candidates regaled his celebrating supporters with the iconic “Up the RA” slogan, referring to the Irish Republican Army, the terror group which fought in the name of uniting Ireland. Another broke into a rousing rebel song commemorating the IRA’s fight with British forces in Dublin.So nearly a century after its partition, is Ireland’s wave of nationalist fervor leading inexorably to a movement to unite one of the last divided countries in Europe? Well, not quite.Despite the unification-themed celebrations, Sinn Fein ran as a populist, anti-establishment party. It won by building a coalition of nationalists, the socially liberal and those who simply wanted to smash the centrist system that’s dominated government for most of the country’s history. Its surge to take the popular vote in last weekend’s election had more to do with a focus on housing than patriotism.‘Momentum Is There’One thing that is clear is that Sinn Fein upended a political order that had seen power swapped between the two main parties — Prime Minister Leo Varadkar’s Fine Gael and Fianna Fail — for much of Ireland’s history since independence from Britain in the 1920s, when the island was divided into north and south.But Sinn Fein does bring Irish unity to the forefront of the political debate — particularly in the wake of the U.K.’s historic, and potentially destabilizing, decision to leave the European Union.“Brexit has changed the nature of the discussion around reunification fundamentally,” said Colin Harvey, law professor at Queens University Belfast. “It’s not going to happen tomorrow, but I’m convinced we are going to have referendums within a decade. The momentum is there.”Ultimately, it’s up to London to call a border poll, and there’s little appetite for such a move anytime soon. But the sands are shifting. It’s been almost a century since the country was split to placate a largely Protestant, unionist majority in the north in the face of increasingly militant demands from the Catholic-dominated south for independence from Britain. By the turn of the 1970s, tension morphed into violence between sectarian groups that left more than 3,500 people dead. Sinn Fein emerged out of that morass.As the political wing of the IRA, the party started to contest elections in the 1980s as part of a strategy known as the “Armalite and the Ballot Box,” mixing violence and elections in pursuit of a united Ireland.The IRA’s tactics horrified many in the Irish Republic. Few openly discussed ending partition for fear of being seen to lend tacit support to the organization, and Sinn Fein struggled to gain much of an electoral foothold in the south, until recent years.‘Sense of Bitterness’Then came the 2016 Brexit vote and the tortured negotiations over how to keep the Irish border free of checkpoints after the U.K. left the EU. That “reawakened a sense of Irish nationalism, particularly in areas close to the border,” said Edward Burke, assistant professor in international relations at Nottingham University, who has examined the effect of Brexit on the British-Irish security relationship.“Brexit showed the British government’s indifference, if not occasional contempt, for concerns around the border question,” he said. “That fuels a sense of bitterness.”In Northern Ireland, after last year’s general election, nationalist lawmakers now outnumber unionists. In the wake of the Sinn Fein surge, former Irish Prime Minister Bertie Ahern described a border referendum as “inevitable.” Yet, huge hurdles exist before the issue could be put on the ballot.“The premise which is being put forward is that a united Ireland could be around the corner,” said Martin Mansergh, a former Irish senator who was a government adviser during the negotiation of the Good Friday Agreement peace deal in 1998. “Well, most people outside Sinn Fein don’t accept that proposition.”Uneasy RelationsUnder the peace deal, the U.K. government can only call a reunification referendum when a vote would likely succeed. As yet, there’s no clear polling showing that there’s enough support in Northern Ireland. Sinn Fein’s emergence could even make a vote on the issue less likely in the near term. The British government is already contending with an independence movement in Scotland, and the prospect of the party steering the emotionally charged process while in government in Dublin “makes it more dangerous and politically unstable,” said Nottingham University’s Burke.In Dublin, too, there’s nervousness about the financial and political consequences. The U.K. subsidizes Northern Ireland to the tune of about 10 billion pounds ($13 billion) a year — about 17% of Ireland’s tax take in 2019. Taking on that kind of obligation could capsize the nation’s finances.Outside Sinn Fein, there’s no huge enthusiasm for the project. Fianna Fail and Fine Gael, which together control close to half to seats in parliament, urge caution.Unionist leaders in Northern Ireland are particularly wary and refused even to attend an Irish government forum on the implications of Brexit in 2016, let alone discuss unity. “Sinn Fein might be just a step too far for many, many unionists in Northern Ireland,” said Mary C. Murphy, a lecturer in politics at University College Cork. “Sinn Fein is the hard edge of Irish nationalism.”\–With assistance from Morwenna Coniam.To contact the reporter on this story: Dara Doyle in Dublin at email@example.comTo contact the editors responsible for this story: Chad Thomas at firstname.lastname@example.org, Chris ReiterFor more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2020 Bloomberg L.P.