When the UK voted to leave the European Union in the 2016 referendum, Ireland was plunged into the heart of the Brexit negotiations. The meandering 300-mile border between Northern Ireland and the Republic would be the EU's only land frontier with the UK. With no free trade agreement possibly for many years between the UK and EU, how would people, goods and services be checked and policed across the frontier?
The UK draft withdrawal agreement, which led to the downfall of Prime Minister Theresa May, provided an answer - the so-called backstop. This guaranteed an open Irish border by envisaging that Northern Ireland would remain tied to EU regulations for the foreseeable future. As a consequence, goods and services could flow as freely as they currently do and no additional border checkpoints would be necessary.
The deal might have been sealed in Brussels in December 2017 had it not been for a last-minute telephone call between Theresa May and the DUP leader, Arlene Foster. Belatedly, the DUP had seen a copy of what was proposed. Mrs Foster said that under no circumstances could her party accept any arrangement which set Northern Ireland apart from the rest of the UK.
"Once we saw the text, we knew it was not going to be acceptable," said Arlene Foster at the time.
From that moment on, the DUP has effectively vetoed the proposed deal which it interpreted as creating a border down the Irish Sea with checks on imports and exports between Great Britain and Northern Ireland.
The DUP and also the smaller Ulster Unionist Party claim any deal which keeps Northern Ireland under EU regulations and rules challenges the country's constitutional position within the UK.
However, the two unionist parties are out of step with majority opinion in Northern Ireland where 56% of referendum voters opposed leaving the EU. Furthermore, leaders of business and agriculture have questioned the DUP's determination to support the leave campaign and argued that Northern Ireland might best benefit from retaining EU links, ensuring an open border and the free movement of goods and services.
Concern runs deep that a no-deal Brexit will damage the livelihood of farmers and businesses, large and small, which trade with Europe and with the Republic. Thousands of small businesses interact north and south. Farmers trade livestock and dairy products. A no-deal Brexit spells tariffs which could decimate trade and lead to closures and job losses.
The Good Friday Agreement, by advocating closer cooperation between Dublin and Belfast, encouraged Catholic nationalists to support power-sharing with Protestant unionists.
Since 1998, nationalists in Northern Ireland have asserted themselves more openly and confidently and come to believe that their aspiration of eventual Irish unity could be achieved by peaceful means.
The spectre of Brexit dividing the Republic within the EU from Northern Ireland outside it, and with the possibility of a hard border in-between, has unsettled many nationalists, virtually all of whom voted in 2016 to remain. Brexit threatens to destabilise peace and afford hard-line dissident republicans an opportunity to whip up terror tactics.
Relations between the DUP and Sinn Fein, the principal parties in power-sharing at Stormont, have deteriorated in the past three years. The fact that the unionist parties appear to be out of step with majority pro-remain opinion in Northern Ireland has even led to demands for a referendum on Irish unity.
The emergence of Boris Johnson in Downing Street has seen much of the emphasis on Brexit turn to his demand for the removal of the backstop. Otherwise he insists the UK will leave the EU on October 31.
The spotlight is now firmly on Ireland. How will the Irish government respond in the certain knowledge that a no-deal Brexit will be disastrous for the economy, because trade with Great Britain is so crucially important? The facts speak for themselves. In 2018, the Republic exported €14bn to Great Britain and imported €18.3bn from there.
At risk is Ireland's agri-food industry, the source of so much of Britain's food table. Butter, cheese, bacon, beef and many other goods would be the subject of potentially crippling tariffs in the event of a no-deal. Much of the Irish exports to Europe flow through the channel ports of England.
However, the Irish have insisted to date that the backstop must remain in place until and unless a trade agreement between the UK and EU makes it unnecessary or alternative means are found to maintain an open border with Northern Ireland.
Brexiteers at Westminster, including the DUP, argue that an open border can be maintained through the use of modern technology to track goods, services and vehicle movements. Brussels and Dublin are unconvinced and argue that such checking systems will take years to perfect.
In Belfast, the unionists maintain the backstop must go. Irrespective of a majority of people in the north wishing to stay in the EU and possibly sympathetic to the backstop proposal, the DUP has argued that unionist consent is required under the Good Friday Agreement for any changes to Northern Ireland's trading relationship with Great Britain.
The removal of the backstop has been the DUP's red-line demand. It remains to be seen whether Boris Johnson can find some formula which can satisfy unionists and, at the same time, find agreement with the government in Dublin.
Will the Irish government blink in the face of increasing pressure from the UK to water down, if not remove the backstop altogether, to avoid the potential disaster of a no-deal Brexit?
Might the DUP soften its demands on the backstop in the knowledge that no one in Northern Ireland wants a no-deal scenario and majority opinion seems in favour of maintaining the backstop to ensure an open border?
By his demands on scrapping the backstop, Boris Johnson has focused attention on Dublin and Belfast. At serious risk are the future economies of the Irish Republic and Northern Ireland if a compromise cannot be found.
At risk too is the whole ethos of the Good Friday Agreement, with its three strands of cooperation - between unionists and nationalists at Stormont, between Dublin and Belfast in ever closer links, and in the wider Anglo-Irish relationship across the Irish Sea.
The Irish government must weigh the now real and obvious danger that insisting on an open-ended backstop, in which Northern Ireland might be tied indefinitely to EC rules and regulations, will almost certainly precipitate a no-deal outcome on October 31.
The DUP must weigh its insistence on scrapping the backstop altogether against the fact that the party does not reflect majority opinion on this issue in Northern Ireland and that, as with the Republic, a no-deal is the worst possible outcome for everyone. With the General Election looming and the DUP no longer holding the balance of power at Westminster, the party cannot exert the same influence as before.
The logical answer to this seemingly intractable situation is to redefine the backstop. Insisting on total adherence to the backstop or demanding that it is removed altogether looks likely to achieve nothing other than no deal.
Finding a compromise on the backstop which may not meet everyone's requirements but is the best that can be achieved for Dublin, Belfast, London and Brussels, may provide a solution, albeit imperfect, for all of them.
Might they agree on a time-limited backstop in their last-ditch efforts to avoid no deal? That will be hard to swallow in Dublin, which has always insisted that a backstop is not worth the paper it is defined upon unless it is open-ended.
The DUP has shown no inclination to date to accept even a time-limited backstop, but that is what many people in Northern Ireland seem prepared to accept. A time limit should also reassure unionists who fear that Brussels and Dublin are trying to lock Northern Ireland permanently into the EU and weaken its British constitutional link.
One way or another 2019 is a defining year not just for Europe but for the future of relationships across the British and Irish Isles. As of now we can only hold our breath and hope upon hope that somehow sense prevails. Ireland looks as if it holds the key. If politicians in Dublin and Belfast can be persuaded to abandon their red-line demands, then the disaster of a no-deal Brexit can still be averted.
Edmund Curran was Editor of the Belfast Telegraph from 1992 until 2005. A longer version of this article appears in Brexit and Northern Ireland: Bordering on Confusion? edited by John Mair and Steve McCabe with Neil Fowler and Leslie Budd, published by Bite Sized Books and available now from Amazon