That is an extraordinary success story and a rare optimistic lesson for the enduring importance of European integration and the transatlantic relationship. Together, European and transatlantic ties provided a special combination of diplomacy, strategy, and incentives to end what many believed was an intractable conflict.

The power-sharing Good Friday Agreement of 1998 that ended the conflict was made possible by three factors: the political investment by the administration of U.S. president Bill Clinton; the rapprochement between Dublin and London; and, in the background, the special “values” role of the EU.

The EU did not play a direct part in the negotiations. But the very fact that Ireland and Britain are members of the EU was important. The EU espouses the values of civil liberties and religious tolerance, not sectarianism and bigotry. By providing a moral framework, it widened the horizon of those in Northern Ireland, the Republic of Ireland, and mainland UK who were caught up in the conflict. That effect should not be underestimated.

For the longest time, the conflict between Irish Catholics and pro-British Protestants in Northern Ireland was fueled by nationalists south of the border who aspired to reunify the island under Irish rule. After centuries of often harsh colonial dominance, many were extremely hostile toward Britain.

Yet before Ireland joined the then European Economic Community in 1973, at the same time as the UK, the Celtic nation was almost completely dependent on Britain for trade and work.

EU membership transformed Ireland. It wasn’t just because of the billions of structural funds money that quickly flowed into the country, speeding up a much-needed modernization of its infrastructure.

It was also because the rest of Europe became accessible to young Irish people. Until then, if they wished to leave Ireland, as many did because of the country’s conservatism or lack of opportunities, they went to Britain or the United States. The EU changed all that, lessening Ireland’s dependence on Britain—and, with it, Dublin’s hostility toward London.

In parallel, attitudes in the highly influential Irish diaspora in the United States changed, too. But there it was a slower shift because of the physical distance involved, which facilitated romanticism and a deep-seated anti-Englishness.

When U.S. president Clinton began to support peace talks in Northern Ireland, he very skillfully brought this diaspora on board. United States–based Irish nationalists who had supported and financed the Irish Republican Army (IRA) realized that the conflict was debilitating for people’s lives, prosperity, and perspectives.

Clinton’s special envoy to Northern Ireland, George Mitchell, exploited this gradual change in the diaspora’s attitude to inspire them with a sense of trust in the negotiations.

There was another dimension to the peace process. Mitchell could lean on an extraordinary rapprochement between the Irish and British governments.

The Irish Taoiseach Bertie Ahern and his British counterpart Tony Blair realized no peace accord was possible without both countries putting behind centuries of British colonialism. That was not easy. The two leaders had constituents on both sides of the divide who opposed any peace deal.

Yet Ahern, Blair, Clinton, and Mitchell persisted. It was one of those rare moments in history when leaders understand that they have one chance to make the world better.

Northern Ireland is not a template for resolving other conflicts. Each clash is sui generis, as Catherine Ashton, the EU’s foreign policy chief, knows.

She managed, against all the odds, to broker a deal between Serbia and Kosovo. One reason for her success was that she had built up sufficient trust in Washington for the United States to let her lead the talks.

Even in today’s mostly peaceful Europe, there remain several more conflicts where the United States and the EU together could change things for the better. Cyprus comes to mind, as does Macedonia.

Americans and Europeans need to regain confidence that their values can help lay old and bitter conflicts to rest. Perhaps this week’s short summit at Lough Erne will be a step in that direction.