Known as the world's most heavily fortified border, the 2.5-by-151-mile demilitarized zone, or DMZ, that spans the border between North and South Korea is dotted with landmines and bunkers and crisscrossed by barbed wire. The strip of land serves at times as a tourist destination, a site for negotiations and one of the most noted potential military flashpoints on the globe.

Although tensions have risen between the United States and communist North Korea in recent months, unease has reigned along the DMZ throughout its existence. It is patrolled by nearly one million North Korean soldiers, while South Korea has fielded some 600,000 troops on its side, coupled with a U.S. force of some 37,000 military personnel stationed under the auspices of the U.N. Command. However, the force patrolling the zone is predominantly comprised of South Korean soldiers.

Before the Korean conflict in the early 1950s, the border between North and South had been set at the 38th parallel. When Japan, which had overrun the Korean peninsula during World War II, surrendered in 1945, troops above the 38th parallel had been told to surrender to the Soviet army, while those below capitulated to the U.S. The Soviets maintained control over the northern region, which developed a Soviet-style communist government.

In the July 1953 armistice that ended the Korean War, the border was moved to the military line of demarcation that lies mostly north of the 38th parallel. The armistice established the DMZ on either side of the line as a buffer between the two countries to prevent further military confrontation. However, the two sides remained at odds for decades, and, despite the armistice, a state of war still exists between the two Koreas.

Clashes in the DMZ
While the DMZ sits at the eye of the storm in the conflict between North and South Korea, it has also incited violence between the United States and North Korea. Ten years after the DMZ was created, North Korean ground gunners forced a U.S. helicopter from the sky when it crossed into North Korean territory. North Korean officials held the two pilots for a year until the United States admitted it had violated the 1953 agreement by crossing the line. Another U.S. Helicopter was shot down in 1969, but the crew was released after 109 days in North Korean custody after the United States again confessed to violating the truce.

One of the zone's most violent clashes came in 1976, when North Korean troops bludgeoned to death two U.S. military officers who had been trimming branches from a tree in the DMZ to improve their view of the North. Five South Koreans and four other U.S. servicemen were killed in the skirmish. According to U.S. accounts, North Korean soldiers initially agreed to the tree pruning but grew violent as the work went on and attacked. The North Koreans said U.S. troops had attacked their soldiers, sparking the battle.

The incident sparked an angry response from President Ford, who accused North Korea of "murder" and warned that Pyongyang would bear full responsibility "for the consequences." The United States raised the readiness level of its forces in Korea and sent a team of soldiers to cut the tree down three days later. According to U.S. officials, North Korean leader Kim Il-Sung issued a statement calling the deaths "regrettable."

However, not all conflicts in the DMZ have occurred above ground. Tunnels dug under the DMZ have caused repeated diplomatic flares between the two countries. A South Korean patrol group spotted the first of four confirmed tunnels from North Korea in 1974. The group saw steam rising from the ground and thought they saw a hot spring, but instead discovered a tunnel only a foot underground, the Associated Press reported. A second tunnel was discovered in 1975.

In 1978, U.N. Command troops discovered a tunnel that North Korea had dug under the border and into South Korean territory near Panmunjom. The tunnel started at the back slope of a hill on the North Korean side of the DMZ and stretched some 246 feet below the surface for nearly a mile, according to a U.S. News and World Report story. The tunnel, discovered by a South Korean counter-tunneling operation after border guards detected underground explosions, was the deepest and largest of those discovered, large enough to drive a jeep through, U.S. Officials said. Although the tunnel is now blocked by a reinforced steel door at the North-South border, the South Korean end now serves as a popular tourist attraction, the Korea Herald reports.

A fourth tunnel was discovered in 1990, crossing some 1,000 yards into the eastern end of the DMZ. U.S. and South Korean officials have denounced all four tunnels as violations of the 1953 truce. North Korea has repeatedly denied accusations they dug the tunnels.

The zone has remained a touchy political subject in democratic South Korea as well. In 1988, South Korean riot police barred the path of a group of 10,000 South Korean students approaching the DMZ from Seoul planning to call for reunification. Some 50 students and policemen were injured in the ensuing clash, while the South Korean government and all three opposition parties urged the students to call off their march, the Economist reported.

Conflict and negotiation
In recent years, bridges between North and South have been discussed, with officials from both Koreas agreeing in 2000 to restore roads and rails reconnecting the two countries. Negotiations on the specifics of such infrastructure redevelopment have yet to be completed.

Some negotiations have been held in the conference room of a building within the DMZ itself that straddles the North-South border.

Despite new attempts at negotiation, however, a tense military standoff continues at the DMZ. In December 2002, North Korea repeatedly brought two 7.62 mm machine guns into the DMZ near the truce village of Panmunjom -- a move that violated the 1953 agreement, U.S. officials said. The armistice permits only small arms and rifles within the zone.

Lt. Col. Matt Margotta told National Public Radio in early January that such North Korean moves are common during times of conflict.

"In the past, when there have been increased tensions, they have used small violations of the armistice agreement to try to create a provocation or a response from the United Nations or the United States," Margotta said.

North Korean officials said the armistice does not apply to the transportation corridor in which the machine guns were placed, a CNN report said. The troops were accompanying a construction crew working in a designated transportation zone to build road and rail links through the DMZ.

In recent years, the two Koreas have attempted to reconnect people as well. When it was built, the DMZ separated families as well as armies; the mines and barbed wire blocked travel and harsh restrictions were placed on communications between North and South. The two Koreas agreed in June 2000 to allow limited reunions of some of the region's estimated 1.2 million family members separated by the border. The first of those reunions came two months later, with 100 people from each side flying to meet family members in the opposing Korea's capital.

Visiting the DMZ
Despite its dangers, the DMZ is one of the Koreas' top tourist destinations, serving as a wildlife and agricultural refuge as well as a living Cold War museum. In a Web posting from 2001, Seoul's Korea National Tourism Organization said some 180,000 people a year visited the zone from the South Korean side.

However, the group warns tourists not to get carried away while visiting the DMZ, warning that disrespect to North Korean guards on the other side of the border could have disastrous consequences.

"This is not London where everyone tries to make the palace guards move using any means necessary. The trick is to keep a poker face: no blinking, no smiling, no flashing a quick obscene gesture, no going cross-eyed to see if you can crack his stone-cold stare. Just don't do it. God forbid one harmless motion from a tourist cause an outbreak of war."

Fewer tourists visit the North's side of the zone, news reports say. Because of strict access restrictions, only around 2,000 westerners visit North Korea each year, the Sydney Morning Herald reports. However, China, which enjoys warmer diplomatic relations with Pyongyang, fields tens of thousands of tourists a year.

In February 2002, President Bush visited the South's side of the DMZ to meet with South Korea's president and with U.S. Troops guarding the region.

-- Compiled by Greg Barber for the Online NewsHour