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President Barack Obama declared peace in Northern Ireland a "blueprint" for those living amid conflict around the world, while acknowledging that the calm between Catholics and Protestants will face further tests. Summoning young people to take responsibility for their country's future, Obama warned there is "more to lose now than there's ever been."

"The terms of peace may be negotiated by political leaders, but the fate of peace is up to each of us," Obama said Monday during remarks at Belfast's Waterfront Hall. The glass-fronted building would never have been built during the city's long era of car bombs.

Obama arrived in Northern Ireland Monday morning after an overnight flight from Washington. Following his remarks in Belfast, he was bound for a lakeside golf resort in Enneskillen for meetings with other leaders of the Group of 8 industrial nations on Syria, trade and counterterrorism. Later Monday, Obama was meeting one-on-one with Russian President Vladimir Putin, British Prime Minister David Cameron and Italian Prime Minister Enrico Letta.

Cameron selected Enniskillen as the site of this year's meeting as a way to highlight Northern Ireland's ability to leave behind a four-decade conflict that claimed 3,700 lives.

Significant progress has been made in the 15 years since the U.S.-brokered Good Friday Accords, including a Catholic-Protestant government and the disarmament of the IRA and outlawed Protestant groups responsible for most of the 3,700 death toll. But tearing down Belfast's nearly 100 "peace lines" -- barricades of brick, steel and barbed wire that divide neighborhoods, roads and even one Belfast playground -- is still seen by many as too dangerous. Obama cited that playground in his speech, lauding an activist whose work led to the opening of a pedestrian gate in the fence.

Acknowledging the reality of a sometimes-fragile peace, Obama recalled the Omagh bombings that killed 29 people and injured hundreds more. It was the deadliest attack of the entire conflict and occurred after the Good Friday deal.

Peace will be tested again, Obama said.

"Whenever your peace is attacked, you will have to choose whether to respond with the same bravery that you've summoned so far or whether you succumb to the worst instincts, those impulses that kept this great land divided for too long. You'll have to choose whether to keep going forward, not backward," he said.

Last month, the Catholic and Protestant leaders of Northern Ireland's unity government announced a bold but detail-free plan to dismantle all peace lines by 2023. British Prime Minister David Cameron formally backed the goal Friday, and Obama followed with his own endorsement Monday.

The president specifically endorsed an end to segregated housing and schools, calling it an essential element of lasting 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 too encourages division. It discourages cooperation," Obama said.

One symbol of that effort to end the segregation was on display as Obama spoke to an audience that brought together students from both faiths, effectively integrating Northern Ireland's schoolchildren if just for a morning.

Drawing on America's own imperfect battle with segregation, Obama recalled how a century after the U.S. Civil War, the nation he leads is still not fully united. His own parents -- a white woman from Kansas and a black man from Kenya -- would not have been able to marry in some states, Obama said, and he would have had a hard time casting a ballot, let alone running for office.

"But over time, laws changed, and hearts and minds changed, sometimes driven sometimes by courageous lawmakers, but more often driven by committed citizens," he said.

Though Obama did not specifically mention Syria, his remarks on Northern Ireland recalled the fierce conflict there that has so far resulted in 93,000 deaths. For those looking for a way out of conflict, Obama said Northern Ireland is "proof of what is possible."

Obama and other G-8 leaders were expected to discuss Syria Monday night over a working dinner. Obama will be looking to Britain and France to join him in sending weapons to the Syrian opposition.

Casting a shadow over the summit are new revelations by the Guardian newspaper that the British eavesdropping agency GCHQ repeatedly hacked into foreign diplomats' phones and emails when the U.K. hosted international conferences, including a 2009 Group of 20 summit in London. The report follows recent disclosures about the U.S. government's own surveillance programs and could lead to awkward conversation as the leaders open another international gathering that Britain is hosting.

Despite an agenda devoted to trade, economic growth and international tax issues, the G-8 will be eclipsed by discussions over how to address the two-year-old civil war in Syria and the decision by the United States to begin supplying rebels with military aid.

Obama's meeting with Russia's Putin later Monday will highlight the rift between their countries in addressing fierce fighting in Syria. While Putin has called for negotiated peace talks, he has not called for Syrian President Bashar Assad to leave power, and he remains one of Assad's strongest political and military allies.

In a likely preview of his discussions with Obama, Putin defended Russia's continuing supply of weapons to Assad's military in a meeting Sunday with Cameron, the British leader.

Putin said Russia was providing arms "to the legitimate government of Syria in full conformity with the norms of international law."

The White House is not expecting any breakthrough with Putin on Syria during Putin's meeting with Obama.

Obama is making his first visit to Northern Ireland, though he visited the neighboring Republic of Ireland in 2011. That trip included a public speech in the center of Dublin, as well as a stop in the village of Moneygall, where Obama's great-great-great grandfather was born. The president called that visit "magical."

First lady Michelle Obama and daughters Malia and Sasha, who also made the trip from Washington, were to spend Monday and Tuesday in Dublin while the president attended the G-8 summit. Later Tuesday, the first family departs for Germany, where the president will meet with Chancellor Angela Merkel and speak at the Brandenburg Gate.