The Irish border wasn’t always so invisible. Between the 1960s and the 1990s, during a period of cross-border sectarian fighting known as “The Troubles,” the heavily-fortified border between the Republic of Ireland and Northern Ireland was far more distinct, outlined by military checkpoints, watchtowers, and customs posts. More than three decades of fighting between the Unionists (predominantly Protestant) advocating for Northern Ireland to remain part of the U.K. and the Republicans (predominantly Catholic) advocating for the North to join the Republic of Ireland culminated in the Good Friday Agreement. This 1998 accord brought an end to the conflict and established a system in which power between the Unionists and the Republicans would be shared. As the fighting between the North and the Republic receded, so did the militarized frontier that once divided them.
“Now if you travel between the Republic of Ireland and Northern Ireland, it’s like driving from New York to Connecticut—you just keep going,” Senator George Mitchell, the primary architect of the Good Friday Agreement, told me. “In fact, it’s hard to even know it now.”
Though the implementation of a hard border certainly wouldn’t resemble the wartime frontier that defined the Troubles, Mitchell said certain aspects, such as the reimposition of border controls, could bring echoes of past division and conflict that might threaten the cooperation the Good Friday Agreement helped achieve. “Commerce has increased, economies have become increasingly integrated … demonization has declined as people move freely across the borders and get to realize they have more in common than that which divides them,” Mitchell said, adding: “A reinstitution of a hard border would set all that back.”
The challenge facing British and European negotiators is how to reconcile the U.K.’s decision to leave the EU with the bloc’s customs union and single market, without implementing a hard border. This is particularly important when it comes to trade between the EU and the U.K. and, more specifically, between Ireland and Northern Ireland. According to a December 2016 report by the U.K. House of Lords, approximately 60 billion euros are traded between the U.K. and Ireland each year, and as many as 30,000 people are estimated to commute across the border between Ireland and Northern Ireland each weekday for work. Between members of the EU, such trade is not subject to tariffs, nor are the individuals crossing the border subject to passport checks.
That all changes, however, once the U.K. formally leaves the EU. “Under EU law, it would end the free movement of people, goods, labor, services, and capital,” Judy Dempsey, a nonresident senior fellow at Carnegie Europe, told me. “Essentially, Northern Ireland would be cut off from Ireland, and Irish trade would be hugely damaged because Ireland in turn would not be able to sell its goods freely to Great Britain, and vice versa, because EU law would have to apply.”