BELTURBET, Ireland — When he crossed into Northern Ireland recently, Patrick O’Reilly felt his body tense up, a feeling that was once all-too familiar but that he thought would never return. Yet now, the fear and anxiety are creeping back, like a long-lost relative suddenly appearing out of nowhere, looking for trouble.
Mr. O’Reilly blames Britain for stirring up those grievances. Its expected departure — possibly a messy one — from the European Union, known as Brexit, is reopening old wounds and resentments in Ireland against its former colonial master.
“The British,” said Mr. O’Reilly, a retired pub manager, as he wove back and forth across the barely detectable border in his car, “are about to kick us in the teeth again.”
In the tortured history between the two island nations, Brexit is just the latest in a long line of perceived slights the Irish have suffered at the hands of the British. And now, with the possible exception of Britain, no country stands to lose more from Brexit, and particularly from a damaging “no-deal” departure, than Ireland.
Not only would that be economically destructive, analysts say; if it results in the return of a hard international border, it could even undermine the hard-won 1998 peace deal with Northern Ireland, known as the Good Friday Agreement.
While the ultimate impact of Brexit is still a matter of debate, there is no question that the issue is stoking tensions between the countries. Barbed comments directed toward Ireland by British supporters of Brexit over the so-called “backstop,” a kind of insurance policy against a hard border being discussed in withdrawal negotiations, have inflamed Irish sentiment.
“The general discourse in parts of the U.K. is extremely arrogant and quite condescending, the feeling that ‘these people don’t know their place,’” said Tony Connelly, European editor of RTE News and the author of “Ireland and Brexit.”
“That, in turn, has awakened a kind of ancient defiance on the Irish side as well,” he said. “All these historical nerve endings that were buried by the Anglo-Irish peace process have reawakened a bit.”
The Good Friday agreement ended 30-odd years of fighting in Northern Ireland, which is part of the United Kingdom, between predominantly Catholic communities that favored joining the Republic of Ireland and largely Protestant loyalists of the British crown, backed by British troops.
During the so-called Troubles, at least 3,500 were killed and relations between Dublin and London were deeply strained.
When Mr. O’Reilly was 18 and growing up in Cavan, a county on the border that is home to much of Ireland’s agricultural industry, five of his friends were gunned down along the frontier just for wearing Irish soccer jerseys.
As memories flooded him, the wooded hills along the road suddenly looked ominous, as if militants could come running out with guns at any moment.
“What would you tell them, that you’re an O’Reilly or a Robinson?” he said, O’Reilly being a Catholic name and Robinson a Protestant one.
An empty farmer’s shed looked particularly suspicious.
“That would have served a purpose, for sure,” he said. “Oh, yes.”
“I had put all of this in the past,” he said, adding of the British: “They’re going to put us back 50 years. The Irish are bullied all the time.”
Many people in Ireland share Mr. O’Reilly’s frustration.
Recent years had been some of the best in memory in Ireland, with the fastest-growing economy in Europe and relations with Britain at an all-time high. But now, last year’s astonishing 7.8 percent growth rate is endangered and the Irish prime minister, Leo Varadkar, recently described bonds with London as “fraying.”
A British government report leaked to the news media calculated that Ireland could see a 7 percent drop in annual economic output, compared to 5 percent for Britain.
While some sectors, like finance and legal services, may benefit from businesses leaving Britain, many others depend heavily on imports of raw materials or parts from Britain. This could mean a double whammy if tariffs are introduced.
On Friday, the Irish government published an omnibus bill to allow people and services — though not goods — to continue to move easily over the border with Northern Ireland in the event of a no-deal Brexit.
“A disorderly Brexit will be lose, lose, lose for the U.K., for the E.U. and for Ireland,” said the Irish foreign minister, Simon Coveney. “We cannot offset all of the damage that it will do, but we are doing all that we can.”
It is the agricultural sector, particularly the meat and dairy producers that account for two-thirds of the country’s total exports, that will bear the brunt of Brexit. Ireland exports about half its beef, a quarter of its dairy products and nearly all its mushrooms to Britain, according to official figures.
The beef and dairy items could be subject to tariffs as high as 70 percent in the event of a no-deal Brexit.
The fall in the pound after the Brexit referendum badly hurt some of the smaller firms. But food producers worry most that if Britain crashes out of Europe, it would open itself to cheaper goods from countries outside the European Union, making Irish firms even less competitive.
Eugene Kiernan runs Breffni Mushrooms, one of Ireland’s biggest mushroom growers, which exports 95 percent of its produce to Britain. The mushrooms are packed in 40-foot containers every day and delivered just a few hours later.
The company lost half a million euros in a matter of hours when the pound plummeted after the referendum, he said. With profit margins of just two to three percent, the company would struggle to survive a possible 12 percent tariff or another drop in the pound, let alone long delays at border posts — fatal for perishable goods like mushrooms.
Even a successful Brexit, from a British perspective, could be damaging to Ireland, said Philip Donohoe, a dairy farmer and a shareholder of a company that makes cream for Baileys Irish Cream.
“If the U.K. ends up doing a trade deal with a country that shoves us out, that could be a big problem for us,” he said.
The British “haven’t thought about the consequences,” of Brexit said Mr. Kiernan, the mushroom grower. “It’s their mind-set. They still think they’re lord and master above everyone else. They come and make all sorts of trouble and leave with all sorts of mess behind.”
The British imperial imprint is still visible in Cavan, which the English took control of in the 16th century under the future King James I. English and Scottish settlers, backed by the crown’s armies, confiscated lands from the native Irish and forced them to adopt English as a language.
“It was tantamount to slavery,” said David Milne, a retired printmaker in Cavan.
Oliver Cromwell, still infamous in Ireland, put down a rebellion in 1641 by Catholic gentry, killing an estimated 20,000. The Irish blame British negligence in part for the Great Famine of the 1840s, when more than a million perished.
From then on through to Irish independence in 1922, Britain ruled Ireland with a heavy hand, assuring that the final battles would be violent. After that came the Troubles in the late 1960s.
Still, relations between Ireland and Britain have vastly improved, particularly since the peace treaty. And in recent years, Ireland has burnished its image as a progressive, modern nation, electing a gay prime minister, legalizing same-sex marriage and repealing a strict ban on abortion last year.
Anglo-Irish relations seemed to reach a peak in 2011 when the Queen paid a visit, the first by a reigning British monarch since 1911, and was warmly embraced by the Irish.
Amid the current strains raised by the Brexit debate, though, a narrative is emerging of “narrow English nationalism versus outward-looking, progressive Irish modernity that sort of has captured people’s imagination,” said Mr. Connelly, the author of “Brexit And Ireland.”
What is most irritating, he said, is that Ireland and the border were hardly mentioned during the Brexit referendum campaign. Now that the border has emerged as the main obstacle to a trouble-free Brexit, he said, Irish insistence on the backstop is drawing toxic responses from Britain.
Jacob Rees-Mogg, a prominent Brexit supporter and Conservative lawmaker, said last month that it would be Ireland’s fault if Britain left the European Union without a deal. Priti Patel, another Conservative politician, drew outrage for implying that Britain should use potential food shortages in Ireland to force it to drop its insistence on an open border.
This is not about crude Britain-bashing, said Diarmaid Ferriter, a historian and author of “The Border.” The British “have a right to vote, but they don’t have a right to ignore the Irish question, because Britain has to face up to its historical responsibilities,” he said. “That can inevitably damage Anglo-Irish relations.”
As the end game approaches, however, Ireland faces a troubling dilemma: Its insistence on the backstop, if it freezes negotiations, could lead to a no-deal Brexit and the imposition of the hard border the backstop is meant to prevent. The closer to the March 29 deadline things get, the greater the pressure will be on Mr. Varadkar to bend.
For all the grumbles and tensions, though, no one in Ireland wants relations to deteriorate more than they already have. The Irish and British economies are so intertwined that what is bad for one is equally bad for the other. And Northern Ireland, unlike England and Wales, voted to remain in the European Union.
“We’ve come a long way down the road,” said John Tevlin, who runs a cattle auction in Cavan, and whose grandfather went on a hunger strike and fought for Irish independence in 1916.
“That’s all in the past,” he said. “We work together and we’re in this together.”