In South Korea, Obama salutes U.S. troops at 'freedom's frontier' Trekking up to one of the last outposts of the Cold War, President Obama on Sunday gazed out over the heavily fortified barrier that cuts through the Korean peninsula and thanked U.S. troops for guarding "freedom's frontier." The visit was Obama's first to the demilitarized zone that has divided North and South Korea for nearly 60 years, and comes at yet another tense point in relations with the secretive nuclear power in the north. Obama met with South Korean and U.S. troops, and like presidents before him, stood in a camouflaged bunker peering through binoculars to inspect the rough, wooded mountains of a nation that has frustrated the West for decades. The president is in South Korea to attend a global summit on securing loose nuclear weapons. But as his Sunday schedule shows, the status of the rogue nuclear program in North Korea is likely to outshine the formal agenda. The DMZ visit was his first stop. Under the new and untested leadership of Kim Jong Un, son of the late dictator Kim Jong Il, Pyongyang has arisen as a fresh puzzle for the U.S. and its allies. Kim surprised many last month by agreeing to halt its long-range missile program in return for much-needed food aid. But the leader seemed to reverse himself soon after by announcing plans to launch a satellite in mid-April. Such a launch would break the deal, U.S. officials say. Japan has threatened to shoot it down. Obama will try to enlist help from the Chinese in persuading North Korea to back off the plan. He's due to meet with Chinese President Hu Jintao on Monday. But first the president headed north about 25 miles from Seoul, beyond the roadblock, mine field and barbed wire fencing to a windswept watch station 25 meters from the demarcation line. Obama looked out from behind bulletproof glass at the two small villages on each side of the line -- Tae Sung Dong, the tiny South Korean town dubbed Freedom Village and Gi Jong Dong, known as Propaganda Village for its fake buildings and speakers that once blared messages trying to lure soldiers to the north. The messages no longer play. And Sunday, Obama looked out in cold quiet as a North Korean flag flew over the village, lowered to mark the end of the 100-day mourning period for the late leader. "There's something about this spot in particular," Obama said in his remarks to U.S. troops. "where there's such a clear line and there's such an obvious impact that you have for the good each and every day that should make all of you proud." The DMZ has long made a dramatic backdrop for a presidential visit, as a rare reminder of Cold War anxiety and America's continued reach. The trip has been one that all of Obama's recent predecessors have made. President George H.W. Bush visited as vice president. President George W. Bush visited the DMZ in February 2002, at another tense time in relations. Bush had just included North Korea in the "axis of evil," a remark that unnerved South Koreans worried about the increasingly bellicose rhetoric. Bush then delivered a toned-down speech and expressed sympathy for the plight of North Koreans. Obama arrived on much better terms with South Korean leaders. During his three-day visit, he's expected to emphasize solidarity with Seoul and make his first comments on the status of the food aid pact. Obama will meet with South Korean President Lee Myung-bak later Sunday.