Journalist Lyra McKee was struck by a bullet fired at police during a riot in the Roman Catholic and Republican area of Creggan near Derry. Her death was a worrying sign of a return to the type of violence that characterized the “Troubles” that ended officially in the Good Friday Agreement of 1998 but have been on the rise since the U.K. voted to leave the European Union three years ago.

DERRY, Northern Ireland — Not a day goes by when Sinead Quinn doesn’t remember how she felt seeing her friend collapse to the ground after she was shot in the head by members of the New IRA, a Republican paramilitary group, six months ago.

“We are in extremism territory again, that's where we are,” said Quinn.

One of the biggest fears for those in Derry and across Northern Ireland is that Brexit will mean the re-establishment of a hard, militarized border between the Republic of Ireland and Northern Ireland. Police fear violent groups like the New IRA, which is driven by an ideological desire to push British officials out of the country and create a united Ireland, are using Brexit to boost their platform.

“This kind of momentum has been building up for some time, but what Brexit does is it pours petrol onto the situation. It is a major accelerant,” Tom Clonan, a security analyst who worked on the border with the Irish army, told VICE News.

Besides McKee’s murder, there have been eight attacks against security forces so far this year, compared to just one in 2018. More broadly, Northern Ireland experienced 56 violent attacks and arrests last year, according to Europol’s latest report on Terrorism in the EU.

In Derry, a former IRA stronghold, there is already a growing sense among working-class communities that they've been forgotten and abandoned by the Parliament in London, and politicians elected to the Northern Ireland Assembly in Stormont, which has not sat for almost three years because of political dysfunction.

"The difference Brexit makes is that it has given them a rhetoric and a language, and a raison d'etre that they didn't have before, and that is gaining traction in the communities that they draw on for their volunteers,” Clonan said.

An old threat returns

For many in Northern Ireland, the horrors and violence of the decades-long struggle between dissident Republicans and the British government came to an end with the signing of the Good Friday Agreement in 1998.