As the 20th anniversary of the April 1998 peace accord for Northern Ireland (known as the Good Friday Agreement or the Belfast Agreement) approaches, concerns are increasing about how the expected exit of the United Kingdom (UK) from the European Union (EU)—or "Brexit"—might affect Northern Ireland. The future of the border between Northern Ireland and the Republic of Ireland has become a central issue in the UK's withdrawal negotiations with the EU. Once the UK ceases to be a member of the EU—likely in March 2019—Northern Ireland will be the only part of the UK to share a land border with an EU member state (Ireland and the UK both joined the EU in 1973). Agreeing upon arrangements for the post-Brexit UK-Irish border is particularly challenging because of Northern Ireland's history of political violence. Roughly 3,500 people died during "the Troubles," the 30-year sectarian conflict between unionists (Protestants who largely define themselves as British and support remaining part of the UK) and nationalists (Catholics who consider themselves Irish and may desire a united Ireland).
UK, Irish, and EU leaders have pledged repeatedly that they will seek to avoid a "hard" border (with customs and security checks) on the island of Ireland to help preserve the peace process and extensive cross-border economic ties. Many in Ireland and the EU, however, question whether and how this will be possible if the UK continues to pursue a "hard Brexit" outside of the EU's single market and customs union. (See also CRS Report RS21333, Northern Ireland: Current Issues and Ongoing Challenges in the Peace Process, and CRS Report RL33105, The United Kingdom: Background, Brexit, and Relations with the United States.)
In 1998, the EU membership of both the UK and the Republic of Ireland was viewed as underpinning the Northern Ireland peace process by providing a common European identity for unionists and nationalists. In the years since, as security checkpoints were removed in accordance with the peace agreement and because both the UK and Ireland belonged to the EU's single market and customs union, the circuitous 300-mile land border between Northern Ireland and Ireland effectively disappeared. This served as an important symbol on both sides of the sectarian divide and helped to produce a dynamic cross-border economy.
Brexit has raised significant political and economic concerns in Northern Ireland (which, unlike the UK overall, voted to remain in the EU). Many experts deem an invisible border as crucial to a still-fragile peace process, in which deep divisions and a lack of trust persist. This situation is evidenced perhaps most clearly by the stalled negotiations between the unionist and nationalist communities' respective political parties on reestablishing the regional (or devolved) government, more than a year after the last legislative assembly elections.
Police officials warn that a hard border post-Brexit could pose considerable security risks. During the Troubles, border regions were often considered "bandit country," with smugglers and gunrunners, and checkpoints were frequently sites of sectarian violence (such violence and criminality have decreased significantly since 1998). Security assessments suggest that if border posts were reinstated, violent dissident groups opposed to the peace process would view them as targets, endangering the lives of police and customs officers. Establishing checkpoints also would pose logistical difficulties. Estimates suggest there are upward of 275 border crossing points.
Many in Northern Ireland and Ireland also are eager to maintain an invisible border to ensure "frictionless" trade and safeguard the North-South economy. Ireland is Northern Ireland's top external export and import partner. Moreover, the two parts of the island share integrated labor markets and industries that operate on an all-island basis.
Figure 1. The United Kingdom and the Republic of Ireland
Source: Graphic created by CRS using data from Esri (2017).
In December 2017, the UK and the EU reached an agreement in principle covering main aspects of key issues in the withdrawal negotiations. Among other measures related to Northern Ireland, the UK committed to uphold the Good Friday Agreement, avoid a hard border (and any physical infrastructure), and protect North-South cooperation on the island of Ireland. In the absence of other agreed solutions that would be preferable to the UK (such as concluding a UK-EU free-trade agreement or devising technology-based solutions), the UK asserted it would maintain "full alignment" with the rules of the EU single market and customs union that support North-South cooperation and the all-island economy. The UK also maintains there will be "no new regulatory barriers" between Northern Ireland and the rest of the United Kingdom.
Nevertheless, questions persist about how such a combination of goals can be implemented. Some analysts contend that an invisible border is impossible unless the UK remains in the EU customs union, a "soft Brexit" option that the UK government rejects. UK Prime Minister Theresa May and the Democratic Unionist Party (DUP)—the dominant unionist party in Northern Ireland—also have adamantly rejected an EU proposal that envisions a "common regulatory area" after Brexit on the island of Ireland. This proposal essentially would keep Northern Ireland within the EU customs union and thereby create a regulatory border in the Irish Sea between Northern Ireland and the rest of the United Kingdom. UK and DUP officials contend this arrangement would threaten the UK's constitutional integrity and thus is unacceptable.
Successive U.S. Administrations and many Members of Congress have actively supported the Northern Ireland peace process. The United States was instrumental in forging the Good Friday Agreement and has encouraged its full implementation over the last two decades. Amid the stalemate in Northern Ireland's devolved government, some Members of Congress have urged the Trump Administration to reappoint a U.S. special envoy for Northern Ireland; the Administration appears inclined to do so. Congress also may consider the possible political, security, and economic implications of Brexit for Northern Ireland, and Brexit's impact on the Irish border and the Good Friday Agreement.