The Belfast/Good Friday Agreement will shortly celebrate 20 years in existence. Many observers, however, are beginning to question if it will survive another 20. The continued stalemate at Stormont and the UK’s exit from the European Union are putting significant pressures on an accord that has power-sharing at its heart.

One key benefit of the agreement was the cementing of a process that ended most physical violence and allowed, eventually, for decommissioning of paramilitary weapons and demilitarisation. This demilitarisation was particularly significant on the frontier with the Republic of Ireland. The Border infrastructure may have gone, but what remains is a more intractable division: a culture war between the communities within Northern Ireland.

The Irish Border has recently returned as a bone of contention in Irish and Westminster politics, which is fuelled by and feeding these divisions between the communities in Northern Ireland. This is due to the UK government’s decision to leave the EU’s internal market and customs union, which has raised the spectre of the return of a “hard border” in Ireland.

All those involved in the negotiations say they wish to avoid this outcome. But despite this cosmetic unity of purpose, the parties are predictably divided along sectarian lines. The DUP supports the British government’s current policy for “hard Brexit”, despite it necessitating, at a minimum, some form of customs checks at the frontier (which the party says it does not want). Meanwhile, the formerly Eurosceptic Sinn Féin opposes Brexit altogether. The Border question is thus exacerbating the already strained relationships between the region’s two largest parties, though this is by no means a recent development.

The DUP has long been focused on the security of the Border. This is understandable, given it was the focus of violent republican energies, and its porous nature was exploited by the Provisional IRA prior to the signature of the agreement. The past campaign of violence on the Border also has a contemporary political relevance, with some unionists claiming that the IRA had engaged in “genocide” or “ethnic cleansing” against the Protestant community in frontier areas.

For these and other reasons, some DUP supporters previously favoured a sealed Border, with only a handful of well-policed crossing points. This, some policy documents contended, would reduce the likelihood of attacks taking place, and allow closer monitoring of those entering Northern Ireland. Indeed, the demilitarisation of the frontier as part of the agreement was one of the key reasons why the DUP opposed that accord.

Alternatively, Sinn Féin strongly supported the normalisation of the frontier, further facilitated by the UK and Ireland’s participation in the EU customs union. Consequently, the outward signs of a British presence on the Border has for years been all but invisible.

Paradoxically, however, the prospect of a hard Border also represents an opportunity for Sinn Féin, as it brings the issue of Irish unification back to the fore. Some perhaps hope that it makes the prospect of unity more attractive, or at least more palatable, to certain non-nationalists. Although this must seem questionable amidst the ongoing disputes about language and cultural identity which are currently preventing the restoration of devolution.

Currently, the DUP seems comfortable accepting the UK’s proposals for a total break with the EU, which will inevitably lead to a hard Border in Ireland. Despite the economic costs, a hard Border may have a psychological appeal for those unionists who feel closer to Camden than Carndonagh. A border might reinforce Northern Ireland’s sense of Britishness and remind Sinn Féin that its ambitions for a united Ireland were thwarted, at least in the medium term. There seems little incentive at present for the DUP, therefore, to abandon its maximalist position.

Things look no more hopeful from the other perspective. One of the more fanciful notions being floated is that Sinn Féin might decide to abandon its policy of abstention at Westminster and use its votes to frustrate Theresa May’s hard Brexit aspirations. Again, there is virtually no incentive for the party to save her government and the DUP from themselves, since the return of the Border would reinvigorate the political struggle for Irish unification. Equally, by remaining outside the Westminster fray, Sinn Féin can deflect blame for any Brexit downsides on to its adversary, the DUP.

The problems for the agreement posed by Brexit therefore are not so much intrinsic to it, but symptomatic of a wider conflict centred on culture and identity that 20 years of relative peace have done little to erode. Thus, whilst the creation of a hard Border might not in itself undo all the progress since the signature of the agreement, it is unlikely to make restoring power-sharing, which is one of its key components, any easier. The consequences for community relations and the durability of the agreement in the longer term seem all too obvious.

Shaun McDaid teaches politics at the University of Huddersfield. This article forms part of #Agreement20, an academic public engagement project organised between the University of Salford and King’s College London, featuring a conference hosted by the Irish World Heritage Centre in Manchester and funded by the Department of Foreign Affairs and Trade on April 6th and 7th, 2018