OBSERVATION POST OUELLETTE, South Korea >> Lt. Col. Edward Taylor stands behind a wall of sandbags overlooking the North Korean landscape and a bank of trees along the most fortified border in the world. The trees obstruct the view, he explains. They need to come down.

But this is the DMZ.

The last time anyone tried cutting trees here was 36 years ago, and it set off a melee with the North Koreans. Two U.S. soldiers were hacked to death with their own axes, touching off Operation Paul Bunyan, a full-scale mobilization of fighter jets, B-52 bombers and an aircraft carrier strike group that brought the two sides dangerously close to conflict.

The axes and clubs are still on display in a North Korean museum near the border as evidence of how the U.S. — Pyongyang claims — used the tree-cutting as a pretext to incite mayhem.

But to this day, the U.S. Army believes the 1976 Ax Murder Incident — North Korea calls it the Panmunjom Incident — was a premeditated attempt to boost the hard-line reputation of Kim Jong Il, who was then being groomed to eventually succeed his father as North Korea’s leader.

With Kim’s own son, Kim Jong Un, now cutting his teeth, Taylor knows his pruning plans could be all that is needed to set off America’s next big war. He commands the U.S. border battalion tasked with monitoring the Demilitarized Zone and providing security.

Though often overshadowed by more pressing conflicts elsewhere — Vietnam, Iraq, Afghanistan, and now the stare-down with Iran — the potential for bloody hostilities on the Korean Peninsula is as real as ever. An agreement announced this week trading U.S. food aid for North Korean nuclear concessions opens a path to broader talks, but challenging obstacles remain.

If war does break out again, the 28,000 U.S. troops in Korea defending a 60-year-old truce arrangement will be right in the thick of it.

"We are in daily contact, sometimes within arm’s reach," Taylor told The Associated Press back in his base camp, named after Capt. Arthur Bonifas, one of the two Americans killed in the 1976 clash. "If something happens, it could happen in minutes."

Maybe, he says, the trees can wait.

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It’s easy to get complacent about Korea. The deadly game of cat-and-mouse on the peninsula hasn’t changed much since the 1976 incident, or for that matter since the 1953 armistice to the Korea conflict.

Crises come and go with numbing frequency.

North Korea pushed the fragile truce to its limits two years ago, when Washington and Seoul say it torpedoed and sank a South Korean warship and later launched a limited but fatal artillery strike on a disputed border island. Pyongyang denies sinking the ship and says the artillery firing was provoked by the South Korean military, which was conducting a live-fire drill nearby.

Washington and Seoul play games of their own.

The United States regularly flies U-2 spy planes out of a base near the border that North Korea views as provocative. U.S. and South Korean soldiers frequently conduct patrols along the DMZ, often at night, that bring them into potentially dangerous proximity to their North Korean counterparts.

The three countries’ militaries are at their most active right around this time of year.

Each year North Korea’s 1.2 million troops, most of them based south of Pyongyang, mobilize for their December-to-April training, which is followed by a lull in the spring and summer as they return to the fields to help plant and harvest. After a brief respite following Kim Jong Il’s death in mid-December, the winter training cycle is just reaching its peak.

This is also when the U.S. and South Korea hold their biggest war games. Some 200,000 South Korean and 13,000 U.S. troops are taking part in the annual Foal Eagle maneuvers that began this week and run through April.

North Korean media have slammed the exercises as an "unpardonable infringement on our sovereignty." On Friday the Supreme Command of the Korean People’s Army expressed outrage over the drills and threatened to wage a "merciless sacred war."

This year’s Foal Eagle is the first since Kim Jong Un assumed power, so Pyongyang’s reaction is being closely watched for signs of how the world’s youngest commander in chief, believed to be in his late 20s, will lead.

Several U.S. commanders interviewed by the AP said there have been no significant incidents. But they added, that doesn’t mean there won’t be.

"We don’t know what is going to happen in the next month or two months," said Lt. Col. David Rayman, commander of the 25th Fighter Squadron at Osan Air Base, 60 miles (100 kilometers) from the border. "We are always exercising. We’re training to the worst-case scenario."

He said his squadron trains in chem gear and gas masks. "We don’t do that in the states. We’re not doing that in Afghanistan. It’s a different war."

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All sides have good reason to avoid another full-on fight. The 1950-53 war killed at least 4 million people, including civilians and troops from the two Koreas, China, the United States and other United Nations combatants. South Korea’s response to the incidents in 2010 was conspicuously measured, and the tensions gradually eased.

Diplomatic efforts to calm the situation continue. This week North Korea, which is believed to have enough weaponized plutonium for four to eight atomic bombs, agreed to freeze most nuclear activities in exchange for food aid from the United States.

But what if cool heads don’t prevail?

Scenarios for how a war with North Korea could unfold range from frightening, if it stays conventional, to catastrophic, if it goes nuclear.

Bruce Bennett, a northeast Asia strategy expert and senior analyst for the RAND Corp. who has advised the U.S., Japanese and South Korean militaries, said any number of triggers could touch that fight off.

Bennett says the battle would unfold rapidly:

—North Korea launches artillery on South Korea’s forward defensive lines and its capital, Seoul, to create panic and a flood of refugees who would clog roads and impede the movement of military units.

The attacks could be laced with Sarin nerve gas and blister agents — North Korea reportedly has 2,500-5,000 tons stockpiled — as commandos infiltrate the South via aircraft, submarines, ships and tunnels under the DMZ.

—South Korea and the U.S. hit back with massive artillery fire, combat aircraft, ballistic missile and special forces strikes. U.S. Marines begin deploying from Japan.

— It could then go nuclear. China would join the fray.

The casualties would be staggering.

"The biggest unique thing is that if anything happens here it’s going to be what we would term a major combat operation — it’s not irregular warfare, it’s not counterinsurgency," Rayman said. "The big deal is that if something happens here, it’s going to be a big fight."

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The stakes are easy to overlook in Panmunjom, up the road from the base camp of Taylor’s border battalion. One of the unit’s most visible missions is protecting — and showing around — more than 100,000 tourists and VIPs who flood the DMZ there each year.

Along with their military duties, soldiers actually act as tour guides for visitors who pour in by the busload, snap souvenir photos of the sky-blue barracks of Panmunjom’s iconic "Conference Row" and absentmindedly sip bottled water as they are lectured on Korea War history. At times, North and South Korean briefers can be seen leading their groups just meters away from each other, on either side of the line.

"People just see us as tour guides with guns," Cpl. Jon West, of Tallahassee, Florida, said as he and about a dozen other soldiers ate dinner at "Sanctuary Club," the Camp Bonifas mess. "It’s really not that. You’re ready all the time."

But U.S. troops in Korea — who go by the motto "Fight Tonight" — are gradually pulling back from the DMZ.

Strapped by more than a decade of expensive wars in Iraq and Afghanistan, the U.S. military is downsizing and preparing for fundamental readjustments under a soon-to-be-slashed budget. Last month, Defense Secretary Leon Panetta announced that will mean a leaner, more agile posture around the world.

South Korea is feeling the changes already. Most of the U.S. forces here are to be repositioned to consolidated bases south of Seoul by 2016. In three years, South Korea will assume operational command — meaning it will be in charge if a conflict erupts.

In the DMZ, the South Korean army already makes up 90 percent of the 750 soldiers deployed to the Joint Security Area. For them and the 70 or so U.S. soldiers who remain under Taylor’s command, life is calm, but uneasy.

"I got here three days before Kim Jong Il died," said Pfc. Jessica Reyes, 23, of San Dimas, California. "I didn’t know what to expect. Even on practice drills, you wonder if maybe this time will be it. It still gets you every time."