DERRY, Northern Ireland >> On a cold, rainy night last January, a group of masked men abducted a 15-year-old boy from his home in Creggan, Northern Ireland, threw him into the back of a van and took him to a dark alleyway. There, they pinned him against a shuttered storefront and shot him in the legs until he collapsed.

The men were linked to one of the region’s main militant groups, the New Irish Republican Army. “They beat me up, I couldn’t breathe and then bang, bang, bang, bang. Everything went blurry and I fell to the ground,” the teenager, now 16, recalled, speaking on the condition of anonymity out of fear for his safety.

“Two of the bullets hit me directly in the shins and two more pierced my thighs. The blood was just pouring out everywhere,” he said, rolling up his tracksuit to reveal the bullet wounds, which have left two crevasses under his kneecaps.

Violence in Northern Ireland has fallen sharply since the 1998 Good Friday agreement formally ended a bloody 30-year guerrilla war between mostly Catholic republicans, seeking unification with the Republic of Ireland, and predominantly Protestant loyalists and unionists, who favor remaining in the United Kingdom.

But now, paramilitary groups that have been lingering for decades are beginning to reorganize, driven by economic stagnation, political paralysis and the potential impact of Prime Minister Boris Johnson’s Brexit plan, which was given a final stamp of approval in last week’s general election after the Conservative Party won a commanding majority in the British Parliament.

Since January, republican militias have targeted police with bombs and mortars, killed a journalist and carried out dozens of “punishment style” attacks on ordinary people in an attempt to take over the policing of deprived Catholic neighborhoods like Creggan.

Violence by Protestant loyalist groups has dropped since the Ulster Volunteer Paramilitary group went on a six-week killing rampage in 2005. But they, too, administer punishment beatings in their neighborhoods.

And Johnson’s Brexit plan was a wake-up call for them, as it would keep Northern Ireland in a customs union with the Republic of Ireland. That would effectively cut off Northern Ireland from the rest of the United Kingdom — a mortal threat to unionists dedicated to preventing unification with the south.

By raising the prospect either of a physical border between the north and the south, which alarms the republicans, or a figurative one in the Irish Sea, which is anathema to the loyalists and unionists, Brexit is fueling unrest in both camps.

“Brexit has put the border in Ireland back into the mainstream in a way in which it hasn’t been since 1998, and ‘dissidents’ are seeking to capitalize on the associated instability and momentum gathering around questions about the border,” said Marisa McGlinchey, an assistant professor of political science at Coventry University in England.

While the new generation of paramilitaries operate in smaller and less sophisticated groups than the militias that fought during the conflict, a spate of attacks this year by republican dissidents with links to the New IRA have stoked fears that they will reignite sectarian tensions.

In the past year, the number of paramilitary-style attacks and deaths linked to paramilitary groups increased, according to a report published this month by the Independent Reporting Commission, a group that monitors paramilitary activity.

The report found that three people had been killed and 81 injured in attacks linked to paramilitary groups in the 12 months ending in September, compared with one death and 75 injuries in the previous period.

“The real issue about the dangers for peace in Northern Ireland is not that Brexit itself could be the direct cause of a renewal of violence, but rather that it has the potential to add fuel to the fire of continued paramilitarism,” the report concluded.

The power vacuum created by the collapse of the region’s governing assembly in 2017 has provided paramilitary groups an opening in poorer areas, where people feel abandoned by politicians amid growing unemployment, rising crime rates, and a housing and health care crisis. House raids and “stop and search” routines by police have also stoked anger among republican youths.

In working-class Catholic neighborhoods like Creggan, republican paramilitaries have taken advantage of the community’s deep mistrust toward the predominantly Protestant Police Service of Northern Ireland to impose their own version of justice.

The teenager who was shot by republican paramilitaries was being punished for stealing a phone and laptop from a store. When residents found him on the night of the attack, lying in a pool of blood, they called a local community worker to take him to the hospital. No one informed the police, including the boy’s mother, who said the paramilitaries would have killed her if she did.

“My mam has no choice,” the teenager said matter-of-factly. “I was let off lightly. If they had found drugs on me, they would have probably blasted my brains out.”

While most of the community condemns paramilitary violence, many believe that the dissidents are more effective at addressing crime than are the police, whom they perceive to be working on behalf of the British state — and therefore against them.

“When some young person is shot today or tonight or whatever, first thing people would say is, ‘That’s awful,’ like that shouldn’t have happened here,” said John Donnelly, who mediates between the paramilitaries and their targets. “But then the second thing they will say is, ‘He didn’t get it for nothing.’ So, there’s a kind of acceptance.”

In recent months, the New IRA has stepped up attacks against the police in Creggan in a bid to stay relevant and attract young people.

“It’s an opportunity for them to recruit,” said Michael Doherty, a local mediator in Derry, a former republican stronghold, “because what they’re saying is politics isn’t working in Northern Ireland, the peace deal isn’t working and it’s not going to work, Britain is still here and we need to use force to get them out.”

Republican paramilitary groups are also preparing for a situation in which they might have to respond to potential violence caused by loyalist protests against the new Brexit arrangement and its border in the Irish Sea.

The proposed sea border is likely to be located in Britain, but analysts warn that the lack of a physical border target could lead to paramilitary sects attacking one another or members of the public.

“Obviously if you don’t have a good target for violence in Northern Ireland, you’ll just go and find a bad one,” said Newton Emerson, a political commentator in Northern Ireland. “That would be the worry that they’ll just start attacking random people or blocking roads.”

In a recent television interview, a masked spokesman for the New IRA said that any British installations or infrastructure on the border or elsewhere would be a legitimate target for attack.

“The IRA is an army, and as an army we are committed to armed struggle for political and social change in Ireland,” he said. At the same time, the political wing of the New IRA, known as Saoradh, has stepped up its recruitment efforts by providing welfare assistance, food and shelter to those in need.

“They are getting stronger because of political paralysis and because of Brexit,” said Ricky O’Rawe, a former IRA member who now helps victims of paramilitary violence. “They are trying to assert themselves, and even though they are not very organized now they do have the potential to put together a concentrated campaign, and that could get dangerous.”

A 43-year-old dissident republican in Creggan with links to the New IRA said he had resisted violence in recent years because he believed that the United Kingdom would fall apart naturally after Brexit, forcing unification with the Republic of Ireland.

“I had some hope for a while, but the peace arrangement is void, it’s one-sided and Brexit is giving the British state more control,” he said, speaking on the condition of anonymity to avoid being investigated by the police. “We have no choice now but to take matters into our own hands.”