The European Union has been a unifying force that transcends the bitter divisions between Catholics and Protestants that have long bedeviled Northern Ireland.
That ends if Britain leaves the European Union.
If British voters opt to quit the EU on June 23, they would undermine Northern Ireland's economy — potentially stoking frustration and resentment among the country's struggling poor — and the 1998 Good Friday Agreement that is credited with curbing violence in the region could unravel, said experts.
"EU integration has been a way to de-conflicting the Troubles," said Edward Burke, a business professor at the University of Portsmouth in the United Kingdom, referring to the decades of violence in Northern Ireland. "It allows all to sit in the European Parliament. It takes this stinging nationalism out of close integration on the island of Ireland."
In addition to years of uncertainly as British and European diplomats negotiate a new relationship, a 'yes' vote for Brexit could also lead to new political crises in the six counties that remained within the United Kingdom after Ireland won independence in 1921.
The partition led to conflicts between Catholic nationalists seeking to join Ireland and Protestant unionists who want to stick with London. Between 1969 and 1999, around 3,500 people died in the conflict, according to the Congressional Research Service.
The 1998 accord led the now-semi-defunct Irish Republican Army's terrorist-cum-freedom fighters and Protestant paramilitaries to decommission their weapons. Catholics and Protestants are still effectively segregated, however, and many former militants have become involved in violent crime.
Today, Sinn Féin, the political arm of the IRA, has called for a plebiscite in Ireland and Northern Ireland to unify the two if the UK leaves Europe. Scottish leaders have similarly called on another vote on breaking away from the UK if British voters pull them out of Europe.
"Sinn Féin might sense there is an opportunity to make a point," said Robert Mauro, director of the Irish Institute at Boston College, noting that while Sinn Féin lawmakers serve in the Northern Irish provincial assembly as well as the national parliaments in Dublin and Westminster, the party has never abandoned its platform of advocating a united island. "There might be more people willing to consider the Republic and Northern Ireland as one entity should the UK leave the EU."
Catholic-affiliated Sinn Féin is in the 'remain' camp.
"There is no doubt that a Brexit would be bad for business, bad for investment, bad for farmers, bad for workers and human rights, bad for communities and bad for Irish unity," said Sinn Féin European Parliament member Martina Anderson in a statement.
The Protestant-backed Democratic Unionist Party, or DUP, the largest party in the Northern Ireland assembly in Stormont, is in favor of Brexit. The British government's official in the region, Northern Ireland Secretary Theresa Villiers, has also broken with her fellow Conservative Party member and boss Prime Minister David Cameron to support Brexit.
British and Irish citizens have been able to travel freely between the two countries with few if any border controls since 1923, DUP Deputy Leader Nigel Dodds told the BBC recently. Dodds said it was a cynical ploy to suggest Brexit would cause the Good Friday agreement to unravel.
"Of all the sort of claims that have been made about threats to the UK and the constituent parts of the UK if we were to leave the EU, I find this claim that Northern Ireland's political stability is going to be undermined is one of the most depressing and disappointing," Dodds said.
But the Good Friday agreement calls for cooperation between Northern Ireland and Ireland, said Burke. Brexit would compel the British and Irish to discuss which barriers they should erect. Those talks could take years, giving radicals who never have supported the agreement time to make their case to renew fighting.
"They would suddenly have a real clear political message: 'The process waged by those people — the traitors, the people who betrayed republicanism, Sinn Féin — these people have gotten you nowhere politically. The only way to get a united Ireland is some form of political action that would include political violence,'" he said.
But Mauro said nobody could make definite predictions — illustrating the problem with Brexit in the first place.
"I think the biggest threat of Brexit is that no one really knows what's going to happen," he said. "Is the peace process going to be upended? I don't really know. You don't want to have that kind of answer to that big a question."
Experts have tallied the economic toll of Brexit on Northern Ireland, however.
Burke published a paper arguing that Northern Ireland has received billions in EU aid for roads, post-conflict counseling for trauma, and agricultural subsidies. Brexit would cause a 3 percent decline in Northern Ireland's gross domestic product, a point worse than forecasts for the rest of Britain.
'Leave' advocates emphasize how leaving the EU would curb unwanted immigration and reassert Britain's identity, said Burke. They tend to avoid the hard talk about lost trade and other problems. "It's impractical," said Burke, who is firmly in the 'remain' camp. "It's economically foolish. The problem is we have a pro-Brexit camp that is promising apple pie for everybody and cream on top."
Around 20 percent of the $1.35 billion in trade that occurs on a weekly basis between between Britain and Ireland would disappear after Brexit, said David D'Arcy, a spokesman for Irish4Europe, a group that is campaigning for the 600,000 Irish-born residents of Britain, including Northern Ireland, to vote against Brexit. A quirk in British law allows Irish citizens to vote in the country. Northern Ireland would be especially adversely affected by the drop-off in commerce, said D'Arcy.
"If they exit the EU, they're going to leave the existing custom arrangement," D'Arcy said. "They will not be privy to the same deal. Any country outside of that club has to pay extra tariffs compared to those who are in it."
D'Arcy didn't necessarily foresee a return to violence in Northern Ireland if Brexit occurs. But he saw nothing good coming from erecting border controls between Ireland and Northern Ireland.
"The border in Ireland is something that through the Good Friday agreement and EU membership has been taken away," he said. "We can live in harmony together, the UK and Ireland, on the same land mass, without a border. The creation of a border for us is a retrograde step."
Follow John Dyer on Twitter: @johnjdyerjr
Image via Wikimedia Commons