Brexit, the British exit from the European Union, has dominated its fair share of headlines in recent years. The process of leaving the EU – and its customs union – will force the United Kingdom to renegotiate policies relating to nearly every aspect of its existence. Included among the troubling consequences of Brexit is the obligation of the UK to tighten what will be its only land border with an EU member state – the border between Northern Ireland, controlled by the UK, and the Republic of Ireland. For the people who live and work along the border, Brexit has threatened an already-tenuous peace and created the specter of a return to the Troubles of years past – particularly, the implementation of a hard border and border controls, the likes of which haven’t been seen in nearly two decades.

Today, a person could cross the border between Northern Ireland and the Republic without noticing. Some 35,000 people cross the 310-mile border on one of more than 200 roads every day. These routes are crucial for both trade and community, as the border runs through the middles of towns, farms, and even homes.

Thirty years ago, however, crossing the border was an entirely different experience. There were only 20 points at which a person could cross, and drivers were required to stop at army-run checkpoints to answer questions about their travels. Camouflaged soldiers hid in ditches watching for suspicious activity, cross-border trains and vehicles were prime targets for bombings carried out by paramilitary organizations, and soldiers occasionally shot and killed travelers with near-impunity.

Checkpoints dotted the border from 1923 to 1993, though the island has nominally been a Common Travel Area since 1922. Today, the Common Travel Area allows citizens of the Republic of Ireland and the United Kingdom to travel freely between the two countries without using a passport, and to access certain “services and benefits in each country such as the right to work, to access public services and to vote in certain elections.

Though officials from UK Prime Minister Theresa May to Secretary of State for Exiting the European Union David Davis have promised to make the continuation of the Common Travel Area a priority, the EU will have as much of a say as the UK when it comes to border regulations. The EU has already warned that, if the UK leaves the customs union, a hard border may be inevitable. The Irish government has already begun identifying locations for new checkpoints, in part because negotiations for the border may continue for years beyond the UK’s official exit. A hard border is likely as a temporary measure during these negotiations, at the very least.

The implementation of a hard border could spell disaster for communities in Northern Ireland and the Republic of Ireland. A return to Troubles-era policy might mean a return to Troubles-era problems – for example, checkpoints and the border have long been a hotbed of paramilitary activity. As a whole, Northern Ireland voted to remain in the EU – which makes these probable changes even more alarming. The people who will feel Brexit’s effects the most wanted no part of it.