KELLY MCEVERS, HOST:
An international border divides Ireland and Northern Ireland. But on the ground, you wouldn't know it. People go between the two countries easily as if they were one. The United Kingdom's decision last year to leave the European Union could change that. People across the island worry about a return to a hard border with customs posts and the possibility of renewed political violence. NPR's Frank Langfitt reports from the town of Claudy in Northern Ireland.
FRANK LANGFITT, BYLINE: Northern Ireland has enjoyed peace for nearly two decades, and for many, the Troubles, the bloody conflict between Catholics and Protestants, may seem like history but not for Mary Hamilton.
MARY HAMILTON: Oh, I would like to move these flowers.
LANGFITT: Oh, OK.
HAMILTON: You know, I think they're - you know, they're withering.
LANGFITT: Do you want some help? I'm happy to help you.
HAMILTON: Yeah, I'll want you to...
LANGFITT: Hamilton is visiting Claudy where nine people died in a series of car bomb attacks in 1972. I'm helping her clear away dead flowers beneath the statue of an 8-year-old girl who was killed that day.
HAMILTON: And one man had lived the second house over, he was just blown to bits at my feet literally.
LANGFITT: And you were injured in the leg.
HAMILTON: I was. I was injured there, and I still have shrapnel in my body that was too deep to get removed, so I suffer every day, so I don't need a reminder to remind me of Claudy.
LANGFITT: Many would prefer not to be reminded of those dark days. But the U.K.'s decision to leave the EU, known as Brexit, has people worried about bringing back old divisions between communities, divisions, they fear, could spark a return to violence.
Good morning, Mrs. Anderson.
MARTINA ANDERSON: Good morning. How are you?
LANGFITT: Nice to meet you.
ANDERSON: Nice to meet you. How are you, Frank, how are you?
LANGFITT: People like Martina Anderson who's a member of the European Parliament and a former member of the Irish Republican Army spent more than 13 years in prison.
ANDERSON: We have had enough of this country being partitioned against the democratically expressed wishes of the people. We are not going to tolerate Brexit.
LANGFITT: Like most people in Northern Ireland, Anderson voted against leaving the EU in last year's referendum. She says any infrastructure along the border could provide a target for those still unhappy with the 1998 Good Friday Agreement, which brought peace after the loss of more than 3,600 lives.
ANDERSON: There would be anger among the people and people will be - groups and organizations would have an opportunity to exploit that. I don't think I need to scare people into realizing we've had a conflict. It was a bloody conflict. We do not want to go back there.
LANGFITT: Neither does the U.K., the EU or Ireland. Simon Coveney's Ireland's foreign minister. He oversees the country's policy towards Brexit and was emphatic in an interview with NPR.
SIMON COVENEY: We cannot accept any re-emergence of a physical border on the island of Ireland. We have had a peace process in place now for 20 years. And one of the significant benefits of that peace process has been a normalization of life on the island of Ireland.
LANGFITT: Some here, though, think a hard border may be hard to avoid. Cathy Gormley-Heenan is a professor of politics at Ulster University.
CATHY GORMLEY-HEENAN: The language is very positive in the sense that they want the Brexit result to do no harm, but the reality is we're left in a very difficult situation.
LANGFITT: Here's why. While the U.K. and Ireland are still inside the EU's single market, goods and people can flow freely between them. But once the U.K. leaves, there could be a need for border inspections and tariffs, which means the border, which disappeared under the Good Friday peace agreement, could re-emerge as a symbol of the island's political divisions. Again, Cathy Gormley-Heenan.
GORMLEY-HEENAN: The most important border is the border in people's minds, the border that actually makes people think that they're different from their neighbor and their friend. So both the EU and the Good Friday Agreement took the border out of Irish politics, and the referendum result put it right in at the heart of Irish politics again.
LANGFITT: Back in the town of Claudy, David Temple stares through damp eyes at the memorial to those killed in the bomb blasts decades ago. He still mourns the loss of his 16-year-old brother William who died while delivering milk here that day. Temple's never recovered from his brother's death.
DAVID TEMPLE: When my brother was killed, I was only 20 years of age. My father died three years later. I worked night and day to keep that family. I took Daddy's place. I suffer from depression and stuff like that. It affects me every day.
LANGFITT: But after nearly two decades of peace, Temple doesn't expect to return to the previous level of violence.
TEMPLE: No, I don't think it'll ever go back to that level because these different terrorist groups will never have the same support among the communities.
LANGFITT: What will the border between Ireland and Northern Ireland look like after Brexit? Right now, it's anyone's guess. The European Union says the United Kingdom must lay out its vision for the frontier's future before negotiations on other issues can move forward. Frank Langfitt, NPR News, Claudy, Northern Ireland. Transcript provided by NPR, Copyright NPR.