A border is coming to the British Isles – just where, though, is not yet certain. This weekend, the leader of the Irish Republic’s nationalist Sinn Fein party called for Northern Ireland to begin preparing for a border poll and a united Ireland. Sinn Fein has been making such calls ever since the Brexit referendum, but only recently have they gained some credibility. The United Kingdom’s imminent departure from the European Union is poised to disrupt the trade and regulatory harmonization that has made the illusion of a united Ireland – and thus the Good Friday Agreement – possible. If the U.K. leaves the EU’s customs union and single market as promised, or leaves the EU without a withdrawal agreement, a border somewhere between the U.K. and the EU is inevitable. The decision of where to place that border will reshape the British Isles and their relationship to the Continent.
The Irish Republic and the EU have been adamant that there cannot be a border in