‘France was France without Alsace and Lorraine...Ireland is Ireland without the North.” Eamon de Valera’s remark to the New York Times in 1963 captured a persistent theme in his thinking about Northern Ireland: once an independent Ireland achieved its potential, it could not fail to attract support from Northern unionists. That belief has been sorely tested by the actual history of the two parts of Ireland, by the violent troubles over three decades to the Belfast Agreement in 1998 and by the gradual but uneven reconciliation between people and states since then. It is now tested in a different way by the Brexit crisis in the United Kingdom.

If the UK pulls out of the EU’s single market and customs union in the forthcoming negotiations, Ireland and Northern Ireland will both be profoundly affected for the worse. The border between us will become the border between the EU and the UK for people and goods, putting at risk the peace, prosperity and reconciliation built since 1998. Ireland and the UK are committed to avoid such consequences. The Government has effectively communicated its concerns to its EU partners and will help give voice to Northern Ireland’s interests in the talks. But the logic of such a radical separation is impossible for the EU to avoid in movements of people and goods even if Ireland and Britain agree bilaterally on keeping them open. A functional commercial border with immigration controls will return in that case.

Brexit is a sovereign decision by the UK. Among the fundamental options it raises is whether Ireland and Northern Ireland should be reunited within the EU. That would better preserve the peace and prosperity both value, many believe. Others disagree, among them most unionists, many Catholics in the North despite their professed nationalism, and also many citizens of the Republic unconvinced by traditional arguments for unity and unwilling to pay more taxes for such a large and uncertain constitutional change.

These questions are posed anew by Brexit in a qualitatively different way to the nationalist-unionist choices that concerned de Valera and generations of those who think like him. Ireland’s interests north and south within the EU may best be preserved by Irish unity if the UK does not hold together under the strain of leaving it. Scotland is a key to that, as its first minister Nicola Sturgeon calls for another referendum on independence.

The future shape of a possible united Ireland badly needs to be explored afresh in these circumstances. The current series ‘Ireland’s call – New Horizons’ in The Irish Times is a contribution to that, opening up several under-researched and little-discussed issues. The work should be continued in an exploratory, non-threatening and inclusive spirit alongside the Brexit negotiations, as part of an equally needed radical reappraisal of Ireland’s future direction and identity.