Paul Moyna keeps two photo albums in the backseat of his cab. Labeled “The Troubles,” they date from 1969 to 1998. The photos inside are at once personal and political accounts: Moyna as a school boy in Belfast; the earliest days of the “Peace Walls” that would come to separate the city’s neighborhoods; and historic snaps of the area, all painstakingly annotated.

If asked for more information about The Troubles, Moyna will pull out a zipped-up bag of rubber bullets, which he keeps in the glove compartment. They’re identical to the ones used by Northern Ireland’s police force to break up riots. (Though designed to bounce off the ground and strike people at about knee level, they eventually killed a total of 17 people. Eight were children.)

When Moyna isn’t driving, he hosts tours of Belfast, with a special focus on the city’s history. He’s a natural guide—voluble, extremely obliging, and good-humored—and he moves from story to story as if circulating among friends at a party. Passengers just looking to go from point A to B also can’t help but get a wider perspective on Belfast from their driver—the city’s settlement by Protestant English and Scottish migrants, how it thrived in the 19th century as a ship-building hub, and its bloodiest moments throughout partition and the three-decades-long Northern Ireland conflict.

While Moyna’s albums have an end date, The Troubles are anything but ancient history. The Good Friday Agreement, which put an end to the conflict, was signed just 20 years ago. Built on a 1994 ceasefire, it’s a complex bit of legislation, but one that, in its fluidity, gave everyone something close to what they wanted. Irish nationalists could have a closer relationship with the south, without compromising British unionists’ relationship with the UK. The agreement is open-ended: Though the Republic of Ireland’s government removed the articles of their constitution claiming sovereignty over the area, there’s a loophole, offering a glimmer of hope to those who dream of a united Ireland. If a majority of the people of Northern Ireland want to be part of Ireland, both the British and Irish governments have a “binding obligation” to make it happen.

Now, the border that once saw so much pain and trauma has become central in the UK’s inability to reach an agreement over its departure from the EU, despite barely featuring in the 2016 referendum campaign mandating that exit. At the heart of it all is the Northern Ireland “backstop” agreement, proposed by British prime minister Theresa May and the EU.

The backstop seeks to avoid a “hard border” of barriers and physical checks between Ireland, an EU member state, and Northern Ireland, which would leave the bloc after Brexit. It’s an emergency measure, designed to allow Northern Ireland to stay in the EU’s custom union if the UK and the EU can’t agree on a permanent solution to keeping the border frictionless, a situation that the UK would not be able to end without the EU’s consent. Brexiteers consider this arrangement, which would keep the UK beholden to the EU for an indefinite period of time, intolerable. May’s proposed deal was comprehensively rejected by the UK parliament last month, and she is currently seeking alternative proposals. The UK will officially leave the EU at the end of March, and if a new arrangement isn’t agreed by then, a hard border inside Ireland goes up overnight.

The backstop is the only option right now that appears to honor the Good Friday Agreement, says historian Margaret O’Callaghan of Queen’s University Belfast, although it’s contrary to “red lines” set by May during Brexit negotiations. “Effectively, if Britain is in neither the [EU’s] customs union nor the single market, it’s really very difficult to see how in any eventuality, there could not be a hard border,” O’Callaghan says.

Lingering aftershocks

The ceasefire may have been declared, and the agreement passed, but the effects of The Troubles linger in Northern Ireland.

While the vast majority of people voted in favor of the Good Friday Agreement, it precipitated a split in the vigilante Irish Republican Army (IRA) between those in favor of the peace process and those against it, who formed the Real IRA. (Since 2012, it has been known as the New IRA.) The holdouts represent an extreme, but volatile, minority who have claimed responsibility for a number of bombings and killings in recent years, in particular against prison officers, police, and drug dealers.

Natasha Frost Houses that back onto a Peace Wall on Bombay Street have large cages to protect from flying debris.

Dozens of Peace Walls divide Belfast and other Northern Irish cities like checkerboards. Locked at 7pm each night for the protection of either side, the barriers divide republican and nationalist Catholic neighborhoods from the predominantly loyalist and unionist Protestant ones next door. Many have murals laying out their stance and allegiance: where nationalists back Palestine, unionists back Israel; Catholic walls are painted in Irish colors, while Protestant murals are emblazoned with Union Jacks.

With less than two months to go before the UK is scheduled to leave the EU, the spotlight has suddenly trained on the politics of these two sides. Northern Ireland’s 1.9 million people are essentially represented in the UK parliament by the eight out of 18 Northern Irish MPs who belong to the DUP, a deeply conservative, Protestant, pro-Union party, which joined a coalition propping up the Conservative party. The DUP was the only party to willingly exclude itself from the process of compiling the Good Friday Agreement. (Northern Ireland’s second-largest party in the UK parliament is Sinn Féin, a left-wing, Catholic party of Irish republicans, that does not take its seats, in opposition to British rule and because its members refuse to swear an oath to the Queen.)

In practice, this means only one part of a deeply segregated country is being represented in negotiations which may affect its economy, and way of life, for generations to come. Where Sinn Féin believe “there is no such thing as a good Brexit,” the DUP spent £282,000 ($370,000) on newspaper advertisements advocating a “Leave” vote ahead of the referendum. Though nearly 56% of Northern Irish voters opted to stay in the EU in the 2016 referendum, the local political party with the most power over the Brexit process is vehemently in favor of leaving.

The Brexit vote isn’t just dredging up resentment about who gets a say, however. Many people in Northern Ireland are actively concerned that the careful equilibrium established by the Good Friday Agreement may be jeopardized by some of the proposed Brexit “solutions.” At the moment, even talking them through is “destabilizing,” O’Callaghan says—in the event of a hard international frontier extending across the country, people may find themselves reappraising their position on belonging to the UK. She doesn’t anticipate any imminent “bombs or armed conflict,” she says, but “if you suddenly feel that you are now in some fortress of the UK, behind what could be an international border, you may feel differently about being willing to remain indefinitely.”

A delicate status quo

The repercussions of The Troubles don’t just lie heavy on Belfast. They’re also present in an ongoing mental health epidemic: Northern Ireland has one of the highest rates of PTSD in the world. Alcohol abuse is chronic, and rising. Heroin use in parts of the country is at epidemic levels, with waiting times to access treatment exceeding 18 months. Though not all of this can be attributed to the conflict and its after-effects—poverty, low employment, and problem debt are other contributing factors—the trauma is still apparent.

Natasha Frost The Peace Walls are richly decorated with graffiti and murals.

At least part of that is due to the country’s uneven economic development, which has left parts of the country flourishing while others struggle. Speaking on the Guardian’s Today in Focus podcast, writer Henry McDonald describes the disparity between these regions, and the strain that puts on regional relations:

We’ve got a huge service sector, but in certain parts of Northern Ireland that hasn’t happened. That hasn’t filtered down. Those left-behind spots, those pressure points that exist are potentially dangerous, in terms of the stability of post-Peace Process Northern Ireland.

Unsurprisingly, these areas are home to disenfranchised youth, ripe for the kind of rhetoric espoused by groups such as the New IRA, which use what McDonald describes as ”political necrophilia” as a means of recruitment. “They say that their generations didn’t fulfill the revolution, that there’s unfinished business,” he says. Now, they say, it is the job of the “new generation” to “pick up the gun and do the same.”

It’s an ideology with “a sting in the tail,” McDonald says, but one that he believes will ultimately fail, recent flare-ups notwithstanding. For most people, there is no appetite for more violence. Even in 1998, war weariness had long since set in: Those who remember The Troubles would hate to see them return, while the younger generation, including McDonald’s own adult children, think of them almost as having taken place “on another planet.”

At 2pm on a recent grey Monday, the local pub is full of men gambling and downing pints. One holds his drink with gnarled hands: the vestige of an IRA-related bombing attempt for which he spent 17 years in jail. A Catholic nun pops by the pub to deliver a Christmas card for the owner, but laughs off requests from drinkers for a blessing. “Being here is blessing enough,” she says.

The pub is around the corner from where Moyna grew up, in a Catholic neighborhood in West Belfast that backs on to a Protestant one. Moyna and his wife—a Protestant—met at the intersection (called the “interface”) at a “recreational riot.” Though Moyna thinks of himself as Irish, his wife and their two daughters would emphatically call themselves British, he says. They have different sports teams, different flags, and different religions. Their political parties are not the same, either, and they would vote differently in a referendum to become one Ireland. Deciding where in the city to raise and educate their two daughters was a head-scratcher, he tells me. “There’s no handbook.”

An unbearable border

For Moyna and his family, as well as for Northern Ireland more generally, life is a delicate, hard-won balance. For the most part, it works—even as some republicans still cling to the idea that they may one day see reunification with the south. When it comes to Brexit, however, it’s hard to understand how many of the options currently on offer could maintain that fragile equilibrium, while keeping promises pro-Brexit politicians have made to their constituents.

Further complicating matters is the fact that the Northern Ireland Assembly, the region’s devolved legislature, has suspended for two years, after power-sharing disagreements between the DUP and Sinn Fein led to its collapse. This puts even more of the onus on the few MPs that Northern Ireland sends to the UK parliament to represent the region’s interests as the Brexit deadline approaches.

At the moment, there is no border between the Republic of Ireland and Northern Ireland: people and goods alike flow as freely as water. Some 30,000 people cross between the two countries each day. Potatoes, to give one classic example, may be grown in the south, brought over the border to the north for cleaning and processing, and then returned back south to be sold to customers. It’s not uncommon for taxi drivers to ferry passengers arriving in one country from the mainland over to the next, while the right to dual Irish-British citizenship means each Northern Irish person can be either, or both.

In the case of a hard border, the supply chain which made Ireland one of the most food-secure nations in the world will have to be reworked. It’s similarly difficult to make sense of how Irish and British people could slip as easily between the two countries without some form of checks. Moyna worries that, as a taxi driver, he’ll be asked to check passports, or held accountable for people moving illegally between the two countries.

Quite apart from being very unpopular, or extremely ill-advised, a hard border would be exceptionally hard to enforce: In a December mapping exercise, the Irish army identified almost 300 crossing points across the 310-mile frontier. Though they claim not to want a hard border, the DUP is under pressure from unionists to oppose anything which might decouple Northern Ireland from the rest of the UK.

British parliamentarians voted recently to force May to re-open Brexit negotiations with the EU and find “alternative arrangements” to the backstop agreement. Within a matter of minutes, the EU said it was not open for discussion, and that the deal would not be renegotiated after more than two years of edits. Neither side seems ready to budge on the issue.

A “no deal” outcome now seems increasingly likely, with no particular provisions for Northern Ireland beyond a promise to wait and see. This week, May reiterated that there was “no suggestion” that the UK would leave without an insurance provision against some sort of hard border in Ireland—though when it came to the details, she said only that technology could “play a part,” and that she was committed to not disrupting the lives of communities along the border.

Belfast lives with hard borders of its own—the Peace Walls that many of its citizens credit with giving them a sense of security. But a countrywide hard border would be unthinkable—even though no one knows quite what the alternative could be. While Brexit would be economically disastrous for the UK as a whole, there are still greater risks for Northern Ireland. Careful legislation may have brought fragile peace to the country, but a “no-deal” Brexit threatens to undo these efforts, and resuscitate a crisis many believed had finally been put to rest.