The border arrangements between Northern Ireland and the Republic of Ireland, which remains in the EU, have been a difficult point, with checkpoints of fears that could damage both economies and undermine the hard-won peace in the North.
Following the evening talks between Conservatives of British Prime Minister Theresa May and her ruling partners, the Democratic Unionist Party of Northern Ireland on the far right, moved to Brussels on Friday where they met with the President of the European Commission , Jean-Claude Juncker.
Speaking with May in the European capital, Juncker said, "we had to make the deal today," as the December 14 deadline approached.
"There has already been enough progress in the three terms of the divorce," Juncker said, referring to the conditions the EU had requested on a number of issues, including the Irish border. Negotiations for the UK to leave the EU can now move on to the next stage.
"This has not been easy for either side," May said. "Reaching this point has required giving and receiving on both sides."
Referring to a point of friction between his party and the DUP, May said: "In Northern Ireland, we will guarantee that there will be no difficult borders, and we will not defend (the Good Friday agreement)."
"No barrier north-south or east-west," he said.
What's on the table?
When the Brexit negotiations began just over six months ago, the EU was clear in its position: it would not tolerate any discussion about a future relationship with Britain until "sufficient progress" had been made on three issues:
– that Britain pays a substantial "divorce law"
– that the rights of European citizens in the United Kingdom are guaranteed
– and that there is no reinstatement of a hard limit between Ireland's North, which will leave the EU with the rest of the United Kingdom, and the Republic of Ireland, which remains in the EU
After tortuous negotiations, the two sides were close to the first two issues, particularly after the United Kingdom. agreed to make a substantial payment to the EU budget, leaving the Irish border as the last obstacle.
It is a historically sensitive issue: the dismantling of border controls and infrastructure was a key point of the Good Friday Agreement, which brought peace to Nor Ireland after years of sectarian conflict.
Although London, Dublin and Brussels seemed to be in favor of Northern Ireland remaining subject to the main European regulations and laws, avoiding the need for border controls, the coalition partners in May did not.
It is not clear what kind of agreement could have been reached with the DUP, but although the May government depends on them to remain in power, the Northern Irish party could also lose a lot if the unstable coalition collapses.  The DUP secured a financing agreement of £ 1.5 billion ($ 2 billion) for Northern Ireland when it agreed to support May, and the government's failure would likely trigger an election that could well lead Jeremy Corbyn's Labor Party to power, who will not be so understanding with the extreme right DUP.
Marilia Brocchetto of CNN and James Masters contributed with the reports.