US President Barack Obama has urged young people in the North to have the bravery to complete the peace process and stand up to extremists.
In his first visit to the North since becoming president, he delivered a strong message of hope and re-affirmed the commitment of the US government to the peace process.
Mr Obama said there was still work to do and that it was the young people in the North who had the power to change things.
In a rousing address at Belfast's Waterfront Hall, he declared that it was up to them if they wanted to stretch out their hands across dividing lines and across peace walls to build trust.
"Peace is indeed harder than war. Its constant fragility is part of its beauty. A bullet need only happen once but for peace to work we need to be reminded of its existence again and again and again," he said.
But Mr Obama also won over the 1,600 schoolchildren who accounted for 80pc of the 2,000-strong crowd in the arena with humour. He joked about his big ears and also told them there were students lounging around in a peaceful Belfast asking each other "what's the craic?".
But he repeatedly made the point that it was up to young people in the North to ensure the peace process succeeded.
"As all of you know all too well, for all the strides you have made, there's still much work to do. There are still people who have not reaped the rewards of peace, there are those who are not convinced that the effort is worth it," he said.
Mr Obama's appeal comes at a time when the divide between many Protestant and Catholic communities in the North is ever present – even though the Good Friday Agreement was signed 15 years ago. And there are now more "peace walls" to separate the communities in Belfast than there were before the agreement.
Mr Obama quoted the "peace comes dropping slow" phrase in WB Yeats's poem 'Lake Isle of Innisfree', but said that did not mean that peace-building efforts should come dropping slow.
"This work is as urgent now as it has ever been because there is more to lose now than there has ever been," he said.
And he told the young people in the audience that they were an example for people in conflict-ridden countries.
"So you are their blueprint to follow, you are their proof of what is possible, because hope is contagious, they are watching to see what you do next," he said.
Mr Obama lightened the mood with a reference to the North's most famous golfer.
"I did meet Rory McIlroy last year and Rory offered to get my swing sorted, which was a polite way of saying 'Mr President you need help'," he said.
He highlighted "segregated schools" as one of the essential issues that had to be dealt with to deliver peace.
"If towns remain divided, if Catholics have their schools and buildings and Protestants have theirs, if we can't see ourselves in one another, if fear or resentment are allowed to harden, that encourages division, it discourages co-operation," he said.
As part of his deeply personal speech, Mr Obama drew a parallel with the segregation experienced by African-Americans in the US. He said when he was a boy many cities still had separate drinking fountains and lunch counters and washrooms for blacks and whites.
"My own parents' marriage would have been illegal in certain states. Someone who looked like me often had a hard time casting a ballot, much less being on a ballot. But over time laws changed and hearts and minds changed," he said.
Mr Obama told the audience that the US would continue to work to boost the North's economy. "To those who choose the path of peace, the US will support you every step of the way."
He referred indirectly to the violent protests by loyalists earlier this year about the non-flying of the Union Jack over Belfast City Hall. He spoke of the "symbols of history that are a source of pride for some and pain for others".
He then concluded on an upbeat note. "As I said on our visit two years ago, I am convinced that this little island inspires the biggest of things. This little island, its best days are yet ahead," he said.
By Michael Brennan Deputy Political Editor