Tuesday, April 10, marks the 20th anniversary of Good Friday Agreement that ended three decades of sectarian bloodletting.

I was there when that deal was made. I felt the warm euphoria and relief of the negotiators as they emerged that morning to bask in the magnitude of their achievement.

Today, their triumph appears sullied: mired not only by its own limitations, but by Brexit, which is polluting the violently toxic brew negotiators thought they had placed a lid on 20 years ago.

The peace deal was no easy concession. More than 3,500 people were killed in what euphemistically became known as "The Troubles." Generations of anger and resentment, dating back centuries, had to be overcome.

On that final night, I waited outside the drab concrete and brick building, tramping the crisp, frost-encrusted grass, trying to stay warm, all the while wondering if there would be a thaw inside, or would the night once again leave patience of the island's citizens unrewarded.

With the help of President Bill Clinton's envoy, mediator Sen. George Mitchell, and the backing of the British and Irish governments, Northern Ireland's deeply divided Protestant and Catholic politicians finally agreed:

The majority of people in Northern Ireland wanted to remain part of the United Kingdom. A substantial number of people in Northern Ireland -- and the majority in the Republic of Ireland -- wanted a united Ireland.

Unionists and Republicans had agreed to disagree and as a result share power in a Northern Ireland Assembly -- known as Stormont -- to run the province.

So weary were residents of a life lived in fear of bombs and paramilitary killings that more than 80% of the population turned out for a referendum on the peace deal, with more than 70% endorsing it.

By any measure, this was progress. Yet today, there still isn't even genuine agreement over what to call the deal. Protestant politicians prefer the Belfast Agreement; Catholic leaders call it the Good Friday Agreement.

The most remarkable achievement of the talks involved two of the most reviled men at opposing ends of the conflict: former Irish Republican Army paramilitary commander Martin McGuinness and the staunchest of Unionists, the Rev. Ian Paisley.

These most arch of rivals overcame extreme personal hatred to share the two top Assembly jobs: deputy first minister and first minister.

So warm was their relationship, in later years they were often referred to as the "Chuckle Brothers." Both have since died of natural causes, and their political tribes almost as distant as they ever had been.

But last January, a political scandal caused Northern Ireland's power-sharing agreement to collapse. As a result, the province has been without a government for 15 months.
What pulled the Assembly down was a lack of trust; what keeps it apart is the essence of the peace deal -- to accept each other's differing identities.

Paradoxically, that's the peace deal's biggest flaw: the fundamentals required to bring communities together just didn't happen.

The province's deeply sectarian school system continues: close to 95% of pupils attend either Catholic of Protestant schools, issuing yet more generations imbued with a segmented view of society.

And its politics remained polarized: Catholic or Protestant, rather than Labour or Conservative, like in mainland UK. Belfast's infamous "Peace Wall" has grown longer since the peace deal, ostensibly so people can feel safer.

Of course, peace deals acting as nothing more than a stop gap is nothing new. The Dayton Agreement in 1995 that ended three years of ethnic killing in Bosnia froze the front lines, but didn't bring divided communities back together.

Northern Ireland's deal also lacked the cementing effect of truth and reconciliation, whereby victims got to hear details -- even apologies -- for acts against them.

A decade ago, I sat with an elderly couple in a Catholic housing estate outside Belfast. We listened to the last words of their son, recorded by the IRA before he was killed, following a confession -- beaten out of him -- that he was an informer.

In a quarter century of reporting from Northern Ireland, it was one of my more painful experiences. Tears poured from the couple's eyes as their son's interrogation concluded with a spoon banging on cooking pot, signaling that he was being taken away to be killed.

The question that struck me then and still does to this day: how could those pains -- and the fears around them -- ever be purged without an honest accounting or even an apology, as happened in South Africa, by all sides for the acts of evil that were carried out?

In all the years since the deal, the IRA, the multiple Protestant paramilitaries known as Loyalists, Northern Ireland's police nor the British state have ever comprehensively owned up to their past misdeeds.

Some have been able to forgive the atrocities visited upon their loved ones. But for many, outstanding injustices grow like clots, clogging Ireland's arteries to recovery.
Into all of this, Brexit has blasted in. The open border between the Irish Republic and Northern Ireland that underpinned the peace deal is in question, just when such doubt is least needed.

To restore the Stormont power-sharing assembly requires a heavy dose of certainty and none of the ambiguity of Brexit: the politics of which both sides believe they can use as leverage to their own advantage.

Once the UK leaves the EU, the 310-mile border that snakes through some of the island's most rugged and inhospitable terrain will become the EU's only land border with the UK. It currently has upwards of 400 crossings.

The way it operates today is vital to the economies on both sides of the border and has become a big political issue south of the border too. The Irish prime minister cannot afford a deal that disadvantages Ireland.

In an effort to placate all sides, British Prime Minister Theresa May has promised the Irish government an open border; the EU regulatory alignment to avoid such a customs border; the Democratic Unionist Party that props her up in Westminster no border whatsoever in the Irish Sea; and the British electorate an exit from the EU's Single Market and Customs Union.

The EU doubts she can deliver on all four promises simultaneously and has demanded she lay out the legal framework for a fallback deal that effectively puts Northern Ireland outside the rest of the United Kingdom's customs framework.

As of this moment, such a proposition could be a deal breaker. The DUP has made clear anything that differentiates Northern Ireland from the rest of the United Kingdom won't get their vote, likely leaving May short of a majority and the UK short of a Brexit deal.

The stakes could not be higher. Today, the threat of a return to violence is very real. Even before Brexit re-opened the Pandora's Box of political demons along the border, paramilitaries on both sides are active. Police are responding daily to attacks, bomb threats -- both fake and real. And gunmen still stalk some streets, executing punishment shootings, much as the IRA did in its hay day.

Yet for all the cooling, there may be reason for hope.

The tail end of troubles seen in the rear-view mirror of an insanely popular Northern Irish TV sit com "Derry Girls" shows that plenty of people are ready to laugh at the quirky nature of their lives.

Since the Belfast/Good Friday Agreement came in to being, its architects have toured the world, touting their success and telling others in conflicts how they, too, can arrive at peace.

At stake now not just the validity of this message, but the UK's place in the world as a problem-solver, rather than a catalyst for drama.

Nic Robertson is an award-winning CNN International Diplomatic Editor whose experience, knowledge and expertise have established his reputation as one of the finest international correspondents in the industry.

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