BELFAST, Northern Ireland — The border was drawn in 1921, splitting communities and sometimes property, as the British government sought to create a home for the majority Protestant population of Northern Ireland at a time when the largely Catholic Republic of Ireland won its independence.

Today, that 310-mile frontier is largely invisible. The only way motorists know they have crossed into Northern Ireland is from the speed limit signs, which use miles per hour measurements, rather than the metric system used in the south. Keen observers might notice a slight change in the pavement as well.

A sign on the border between Northern Ireland and the Republic of Ireland, spray painted with the initials of the Irish Republican Army, alerts drivers to the change in miles per hour for speed limit postings, Tuesday, Dec. 17, 2019, in Newry, Northern Ireland. (Credit: David Goldman/AP.)

An old railway bridge blown up by the British Army in the 1970s is partially submerged in the Belcoo River that separates Northern Ireland from the town of Blacklion, Republic of Ireland, Monday, Dec. 23, 2019. The 310-mile border between the Republic of Ireland and Northern Ireland will be the United Kingdom’s only land border with an EU country once Britain leaves the now 28-nation bloc. (Credit: David Goldman/AP.)

As Brexit takes effect Friday, residents on both sides of the border are concerned about protecting the relative peace and prosperity after the 1998 Good Friday Agreement. That accord helped end three decades of sectarian violence between paramilitary groups that wanted to reunify Ireland and those who insisted the six counties of Northern Ireland should remain part of the U.K.

A pedestrian walks by St. Mary’s Catholic Church, Sunday, Dec. 22, 2019, in Aughnacloy, Northern Ireland. Northern Ireland’s six counties are part of the United Kingdom. Most of its Catholics, historically discriminated against, sought unity with the Republic of Ireland to the south. They became known as nationalists, or republicans. Most Protestants insisted on remaining in the union, and became known as unionists, or loyalists. (Credit: David Goldman/AP.)

Members of the Orange Order including Nigel Dawson, left, and Dean Elliott, are stopped by police while marching down the road in front of Drumcree Parish Church as part of their weekly protest against a ban on them continuing on through a Catholic area, Sunday, Dec. 22, 2019, in Portadown, Northern Ireland. The weekly protests have continued since 1998 when the Protestant group was last permitted to complete their traditional route through a Catholic area and is viewed by some groups as controversial. (Credit: David Goldman/AP.)

Lisa Partridge, a 28-year-old tour operator raised in a British military family, remembers how it was “completely normal to check under the family car for a bomb every morning before you went to school.”

“Nobody would want to go back to that life,” she said.

Central to the deal was the fact that both the U.K. and the Republic of Ireland were EU members, which allowed authorities to tear down hated border posts that had slowed the passage of people and goods as police and soldiers tried to halt the flow of arms and militants. With the end of onerous border controls, trade flowed freely between north and south spurring economic development in both communities.

An old British telephone booth sits on the side of a rural road, Monday, Dec. 23, 2019, in Aghnablaney, Northern Ireland. (Credit: David Goldman/AP.)

A mural commemorating a Protestant infantry division fighting in World War I’s Battle of the Somme, in which both Catholics and Protestants fought a common enemy, decorates the side of a housing complex, Thursday, Dec. 19, 2019, in Portadown, Northern Ireland. The mural replaced a loyalist painting showing scenes of illegal gun smuggling and firearms training and was an attempt to tone down the confrontational message and reconcile community relations. (Credit: David Goldman/AP.)

The British and Irish governments have promised to preserve those gains, but people on both sides of the border are concerned that Brexit may re-ignite tensions.

“Who’s to know what way it’s going to go?” said Gary Ferguson, 27, as he milked the cows on his father’s farm. “It’ll make us or break us.”

Signs of the conflict, known here as “The Troubles,” are still evident, even if rust and moss have softened their hard edges.

In the village of Belcoo in Northern Ireland, an old railway bridge blown up by the British army sits partially submerged in the river that separates Northern Ireland from the town of Blacklion in the Irish Republic. An old customs post splits the small village of Pettigo between north and south. In Belfast, “peace walls” still seek to prevent violence by separating Protestant and Catholic neighborhoods.

Lisa Partridge, 28, who grew up with the Protestant Loyal Orange Institution, is reflected in a portrait of Queen Elizabeth II at the Orange Hall, Thursday, Dec. 19, 2019, in Portadown, Northern Ireland. “I grew up within the military family. It was completely normal to check under the family car for a bomb every morning before you went to school, like it was just normal, normal military life,” said Partridge. “Nobody would want to go back to that life.” (Credit: David Goldman/AP.)

Pharmacist Tom Murray, 46, stocks shelves at his pharmacy in Castlefinn, Ireland, just over the border from Northern Ireland, Monday, Dec. 23, 2019. “My historical political view, I think Ireland should always be united country and should be free of the shackles of Britain. But at the same time, we have to accept that there’s one million people living a mile away who identify as British,” said Murray. “I think we have to protect their identity, their culture, their Britishness every bit as much as we have to protect my Irishness. Otherwise it just won’t work.” (Credit: David Goldman/AP.)

To ensure there would be no hard border between north and south, British Prime Minister Boris Johnson agreed to different rules for trade between Northern Ireland and the EU than those that apply to the rest of the U.K.

Unionists see this as weakening the ties between Northern Ireland and the rest of the U.K., raising concerns that the reunification of Ireland is now more likely.

In Portadown, the Protestant Orange Order still holds weekly protests to assert its British identity.

“This is Britain. (It) says so on the map,” said David Reid, 33, walking in Belfast with his 1-year-old son in the shadow of a peace wall that separates his Protestant community from a Catholic one. “Me personally, it just doesn’t feel like it. It feels like you’re down in Ireland.”

Musicians play at the John Hewitt, a bar opened by a nonprofit with the intent of bringing together communities by providing services for the unemployed and is a popular gathering spot for artists, both Catholic and Protestant, Saturday, Dec. 21, 2019, in Belfast, Northern Ireland. (Credit: David Goldman/AP.)

Adrian McSorley, 50, tends to his sheep on his farm, Monday, Dec. 23, 2019, in Scraghey, Northern Ireland. “We’ve been getting a subsidy from the EU for farming. Whatever happens, we’ll just have to get on with it,” said McSorley whose lamb meat ends up south of the border. “But, if there isn’t a subsidy for farming, it’ll become non existent.” (Credit: David Goldman/AP.)

On the other side of the border in Castlefinn, in Ireland’s County Donegal, Tom Murray runs three pharmacies and says his primary goal is to protect the economic gains of the last two decades.

“I think Ireland should always be a united country and should be free of the shackles of Britain,” said Murray, 46. “But at the same time, we have to accept that there’s 1 million people living a mile away who identify as British. I think we have to protect their identity, their culture, their Britishness every bit as much as we have to protect my Irishness. Otherwise it just won’t work.”

Gerry Storey, 83, of the Holy Family Boxing Club in Belfast has been working to bridge the divide by bringing Protestant and Catholic youths together in the boxing ring.

“When you come in here, you don’t talk politics. You don’t swear. And there’s no football jerseys,” Storey said. “In here everybody is treated fairly and squarely. And it doesn’t care who or what you are.”

Ferguson, a fifth-generation Protestant dairy farmer in Stewartstown, Northern Ireland, agrees: “Irish, British, it doesn’t matter.”

“As long as the farming stays OK, that’s all,” he said. “And no wars start.”

Gerry Storey, left, an 83-year-old Catholic trainer at the Holy Family Boxing Club, spars with Jack Douglas, a protestant 19-year-old from Antrim, Friday, Dec. 20, 2019, in Belfast, Northern Ireland. “What we are doing here is really essential,” said Storey, of the club’s long history of training both Catholic and Protestant boxers together. “When you come in here, you don’t talk politics. You don’t swear. And there’s no football jerseys. In here everybody is treated fairly and squarely. And it doesn’t care who or what you are.” (Credit: David Goldman/AP.)

David Reid, 33, walks with his son Lawson, 1, in front of their home bordering a wall separating their Protestant neighborhood from a Catholic one, Saturday, Dec. 21, 2019, in Belfast, Northern Ireland. “It will go back to the troubles then because there be too many fighting on the street if it was a united Ireland,” said Reid. “I’m proud. Just proud to be British and I love my British culture. This is Britain, says so on the map. Me personally, it just doesn’t feel like it. It feels like you’re down in Ireland. I think no matter what if it did end up being a united Ireland, I think we would end up going.” (Credit: David Goldman/AP.)

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