"These people gave you a gift", he said.
The historic agreement, which was signed on April 10, 1998, was reached after several years of talks between political parties and nearly 30 years of violence.
Among other things, the agreement established a power-sharing government involving parties representing both the majority Protestant population and minority Catholic population; it removed border security between Northern Ireland and the Republic of Ireland; and it eventually led to the decommissioning of the weapons of the Irish Republican Army and Protestant paramilitary organizations.
Twenty years on from the Good Friday Agreement, with Stormont mothballed, direct rule looming and the future unclear, the numbers make for grim reading.
"Remember you inspired the world 20 years ago, you can do it all over again because the rest of the world continues to do foolish things - you do smart things".
Clinton urged all sides to make "whatever compromises have to be made to minimise the damage of Brexit". Bill Clinton says peace needs constant work.
Sky's head of data, Harry Carr, said: "If a post-Brexit deal that avoids border controls either on the island of Ireland or in the Irish Sea can not be found, Theresa May will clearly have a problem on her hands".
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He stressed that the US tariffs on China were simply proposals, still to be vetted by trade officials and open to public comment. The yield on the benchmark 10-year Treasury note settled at 2.830%, up from 2.788% on Wednesday.
Britain's solution is to keep open the nearly 300 roads that connect Ireland and Northern Ireland, but to impose a "virtual" or "cyber border" for goods and ID checks after Britain and Northern Ireland left the EU.
Noting the aims of the Good Friday Agreement - addressing "contentious political problems in the context of decades of violence, divided communities and enormous suffering and death" - the Primates acknowledged the complexity of the document, adding that it was also controversial in places.
"But 20 years is a short time and the role of the border in our history, our attitudes, and, yes, our politics is still vivid - it's like the touch-paper of a firework", he added.
He concluded: "In his Nobel Prize speech Seamus Heaney also said of WB Yeats that his intent was to clear a space in the mind and the world for the miraculous".
Ahern voiced regret about Brexit more broadly speaking. "But that's the way it is", he said.
Brexit "changes what has otherwise been the symmetry of relations between Ireland, the United Kingdom and Europe - that is now broken if Brexit goes ahead", Blair told journalists in London.
"The symmetry of relations between Ireland, the United Kingdom and the European Union will be shattered by Brexit", he said.