A top White House adviser during the Troubles has appealed for the next generation not to inherit the hatreds of the past.
Nancy Soderberg - one of Bill Clinton's key strategists during the peace process in Northern Ireland in the 1990s - said the ending of violence there has been a shining example to the world.
She met international pupils at a summer school in the Clinton Centre in Enniskillen, which she said embodies the president's legacy of peace in Northern Ireland.
The centre is next to the town's war memorial where the IRA killed 11 people in a Remembrance Day bomb attack in 1987. More than 60 people were also injured, and a 12th person died some years later from his injuries.
"Today, 15 years after the Good Friday Agreement, the peace process remains a difficult one, but it is irreversible," she said as the G8 started in the nearby Lough Erne Resort.
"The institutions are slowly working, but the pain of the Troubles remains, slowing the trust, impeding a fully integrated society. Those peace walls are still up. But progress will continue, the peace will hold, the hatreds will recede. We will ensure the next generation does not inherit the hatreds of the past."
Ms Soderberg described the Enniskillen blast as one of the darkest days in history.
"Today, it stands as a testament of a determination of the Irish to end decades of violence, violence that claimed more than 3,000 lives," she said. "It stands as a testament to the courage and determination of the leaders that saw a different Ireland. One of tolerance, one of peace, one of unity."
The former US ambassador to the United Nations paid tribute to several political figures from Northern Ireland, Britain and the Republic of Ireland, and the men and women nationwide, who worked everyday for peace.
"During the Troubles, no one came to visit Northern Ireland," she said. "Today, the leaders of the G8 are arriving for their annual meeting to discuss the key challenges of today. That is the legacy of President Clinton."