Jim McCann, the vice principal of St. Joseph’s Primary School, made his way through the hallways, pointing like a proud father to the colorful paper butterflies crafted by his students that hung from the ceiling.

He cheerfully greeted each child by name as he passed them. Then he stuck his head into a classroom, where the students addressed him in unison, “Good afternoon, Mr. McCann!”

The school is in the largely Catholic Falls Road area of west Belfast, which was engulfed for decades by the bloody sectarian struggle in Northern Ireland known as the Troubles. Outside, where multicolored fencing provides a bright backdrop to children playing soccer in the yard, gunfire once ricocheted, with army snipers perched on rooftops and armored vehicles rolling by.

But since peace took hold here 25 years ago, the neighborhood feels worlds away from that past. To Mr. McCann, 68, the transformation mirrors his own evolution.

The now-vice principal spent decades involved in the Irish Republican Army, or I.R.A., a paramilitary organization that used violence to try to end British rule in the region. He was convicted of attempted murder and spent nearly 18 years in prison.

Like many of his generation, Mr. McCann’s life was shaped not only by the Troubles, but also by the peace process that eventually ended the conflict.

“There is no need for violence whatsoever now, and those who are still involved in it aren’t doing anybody any favors — they are holding progress back,” he said, in his office at the school earlier this year.

Many Catholics in Northern Ireland have held a nationalist and republican dream for more than a century: undoing the 1921 partition that kept Northern Ireland under British rule and reuniting the territory with the Republic of Ireland. That vision has at times left them in violent conflict with the mostly Protestant unionists and loyalists who believe the area should remain part of the United Kingdom.

Mr. McCann’s ties to the republican movement began after a series of deadly crackdowns in the late 1960s and early 1970s on civil rights marches in Belfast and Derry. At those marches, Catholics protested against discrimination by the Protestant-controlled government and police forces.

As the tensions deepened, communities divided along sectarian lines, and paramilitaries sprang up on both sides. Still a teenager, Mr. McCann watched as the city around him became a war zone. Ignoring his parent’s protests, he joined the I.R.A.

“It was a very strong sense of community, being part of that and the community asserting itself,” he said. “And you knew there was no going back.”

In 1976, when he was 19, he was arrested while on an I.R.A. operation, driving a stolen motorcycle as another man fired off the back at a police officer. The officer was injured but survived. After Mr. McCann’s conviction of attempted murder, he was sentenced to 25 years in prison. He was released in 1994.

By the time the peace accords known as the Good Friday Agreement were signed in 1998, some 3,600 people had died in the conflict.

While Mr. McCann doesn’t glorify the violence of the Troubles, he believes it was a necessary part of a struggle for a more equal society.

“I never, never, never, ever regretted it and have always been proud of what I was involved in,” he said. “I’ve led a very fulfilling life even though I was in jail.”

Robert J. Savage, a professor at Boston College and an expert in modern Irish history, said that to some unionists, “the notion of a former I.R.A. prisoner working in a school with young children would not be acceptable. It would be upsetting.”

While peace has firmly taken hold, memories of the Troubles haven’t fully faded.

“The violence might be over, but there is still this trauma below the surface for many people,” Professor Savage said. “And the I.R.A. was part of that violence, and society remains divided.”

There has been “a real lack of accountability,” in the years since the peace accords, he said, adding, “That’s been a bitter pill for people to swallow, and not just for victims of the I.R.A. but for victims of the British-backed security forces.”

In 2021, Mr. McCann published “6,000 Days,” a memoir of his time in Northern Ireland’s notorious Maze Prison. The book chronicles the daily experiences of the hundreds of I.R.A. prisoners who protested through a series of increasingly extreme, sometimes fatal, measures, like hunger strikes. It also describes a high-stakes prison break that saw 38 men escape. Mr. McCann and 18 others were recaptured within 24 hours.

The details he shares are stark. For years, the men, including Mr. McCann, refused to wear prison uniforms in an act of defiance, becoming known as the “blanket men.” They staged a “dirty protest,” smearing their excrement on the walls. They were beaten by guards who turned fire hoses on them.

Mr. McCann wrote of the grief of watching 10 fellow I.R.A. prisoners die in the hunger strikes of 1981. For those sympathetic to the republican movement, even those who disavowed the violence of the I.R.A., the deaths drew great sympathy and would mark a turning point.

Later that year, the protests were called off and a compromise allowed prisoners to wear their own clothes.

In prison, Mr. McCann struck up a deep friendship with another I.R.A. member, Joe McDonnell, the fifth man to die in the hunger strike. Mr. O’Donnell attended St. Joseph’s as a boy and is seen as a hero in the neighborhood’s largely republican community. A plaque near the school gates bears his name. It’s a daily reminder to Mr. McCann of his friend, the area’s violent history and the hopes for a conflict-free future.

Mr. McCann was 38 when he was released from prison as part of the peace process. He soon became a father of three, got married and then, after earning his college degree while imprisoned, became a teacher.

“My father was a teacher, and from a young age, I always knew that’s what I wanted to do,” he said. “For all those years, it was what I knew I wanted.”

Many of his students’ families had personal connections to the conflict, and some experienced the worst of its fallout, with family members killed.

“They are a diverse group,” he said of his students, pointing out that the decades of peace have brought immigrant families. “But you still have the separation between Catholics and Protestants. Unfortunately, we do still have it. We’re still separated.”

Sitting in his childhood home, Mr. McCann looked over relics of his prison life, including small slips of toilet paper, covered in tiny, neatly written lines of text, where he had scrawled messages to friends and family to be smuggled outside.

While he’s still involved in the politics of the republican movement, Mr. McCann says he is committed to a peaceful pursuit of that goal.

“I realized that the military side of the struggle had run its course,” Mr. McCann said. “It took us so far and it wasn’t going to take us any further.”

He has campaigned for Sinn Féin, a party that was once the political wing of the I.R.A. but that renounced violence and engaged in the peace process. Once on the political fringe, Sinn Féin has risen to become a force, winning the most seats in Northern Ireland’s 2022 elections.

On an afternoon in early February, Mr. McCann went to the Great Hall of Stormont, Northern Ireland’s government building, to see Michelle O’Neill, a Sinn Féin politician, make history when she became the first republican First Minister of Northern Ireland, the top job in the power-sharing government.

Ms. O’Neill has described herself as someone who, like Mr. McCann, represents “the Good Friday generation” committed to cooperation and peace.

It was a moment Mr. McCann thought he might never see.

“It was good to be with people who have spent the vast majority of their life, certainly their teenage and adult lives, struggling not just to get us into Stormont, but to help us progress toward our ultimate objective, which is a united Ireland,” he said of the other members of the republican movement he stood alongside that day.

“But in the interim, to make this a place where everyone can live reasonably happy, that is a place of equality, that is a place of opportunity,” he said. “That’s what matters.”

Audio produced by Parin Behrooz.

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