evidence: But with Northern Ireland and the rest of the UK having officially left the EU, this has changed. Throughout Brexit negotiations, EU, Irish, and UK officials all sought to avoid the return of a hard border, fearing that checkpoints could complicate trade, revive tensions between communities, and open the door to renewed violence. Yet London’s commitment to leaving the EU single market and customs union made some sort of border checks inevitable. The new relationship between the EU and the UK, negotiated over the course of 2020 and implemented starting in January 2021, settled on a complicated solution to this thorny problem: the Northern Ireland Protocol. What is the debate over Brexit’s Northern Ireland Protocol? Like the rest of the UK, Northern Ireland is no longer part of the EU customs union, the basis for common tariffs on all goods entering the bloc. That means customs checks are necessary. However, to avoid a hard border with the Republic of Ireland, those checks instead take place between Northern Ireland and Great Britain; this, in effect, creates a new border in the Irish Sea. Meanwhile, Northern Ireland—but not the rest of the UK—continues to follow many of the EU’s single-market regulations, allowing the land border with Ireland to remain open. Additionally, the protocol is aided by a separate Ireland-UK agreement that allows free movement of people between the two countries.