"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)."
CRS Insight, IN10869