Three years ago, Colombian President Andres Pastrana - elected on a wave of clamors for peace - granted the country's largest insurgent group a vast haven to facilitate negotiations toward resolution of South America's longest and deadliest guerrilla war.
Today, as the Revolutionary Armed Forces of Colombia (FARC) vacates the Switzerland-size zone that Mr. Pastrana has ordered the Army to take back, Colombians wonder nervously if what was once dubbed a "laboratory for peace" was not instead a training ground for even more devastating warfare.
After years of sporadic peace negotiations, the FARC, the Army, and resurgent paramilitaries are in fact stronger in numbers, financing, and arms - and most observers foresee a period of heightened violence for the 40-year-old war.
In the past three years, thousands of ordinary Colombians attended meetings in the safe zone to discuss issues such as land reform and oil policy, but the government and FARC never so much as reached a cease-fire agreement. The only tangible result of the talks was a prisoner exchange last May, while fighting continued throughout the rest of the country.
Using the enclave as a training ground for new recruits, the FARC has grown over the past three years, now fielding some 17,000 well-
armed fighters. The group is unlikely to fight Army forces as they move in to reclaim the demilitarized zone, but are likely to withdraw to the jungle hideouts they used before the talks began. Jason Hagen, a Colombia expert at the Washington Office on Latin America, predicts that the guerrillas will intensify their trademark actions: kidnappings, bombings, and the destruction of infrastructure.
Meanwhile, he says, the right-wing paramilitaries have nearly doubled to some 8,000 troops, and are expected to direct their attacks exclusively against the civilian population.
Government forces have received $1.3 billion in US military aid, mostly in the form of combat helicopters. The aid was given in the name of the US war on drugs, but with both rebels and paramilitaries depending on drug money, the lines between counternarcotics and counterinsurgency have grown increasingly blurred.
"In a war that hits particularly the civilian population, it'll be more of the same, but with a wider scope and intensified," Mr. Hagan says. "More intense and crude."
Analysts say that despite US backing, the Colombian military still is not strong enough to defeat the FARC on the battlefield. Although the rebels have little support in urban areas, they currently operate in around 70 percent of the country's rural hinterland, where centuries of neglect by the central government has left a fertile ground for the revolutionary cause.
Despite a last-ditch intervention by the United Nations, Pastrana has rejected a rebel proposal to resume peace talks. As government forces massed outside a rebel enclave, a United Nations peace envoy admitted that intense weekend negotiations with the FARC had failed.
Speaking outside the thatch-roofed hut where he met with guerrilla commanders, James LeMoyne said that both sides had a "desire for peace." But, he added, "Reaching peace is not easy, and in the present circumstances it is very difficult.... It is possible that we will not achieve what we hope for, which is peace."
On Sunday, a senior FARC commander read a communiqué which effectively put an end to the failing peace process. The government ultimatum, giving the FARC until 9:30 last night to withdraw 8,000 fighters from the demilitarized zone, "unilaterally changes everything which has been agreed in the past three years, and so closes the possibility of a peace process," read Simon Trinidad, a FARC commander and a member of the negotiating team.
Despite weekend negotiations, guerrillas were already abandoning their positions. At a camp near the negotiation site, all that remained of this peace experiment was a discarded copy of the Communist Party newspaper Voice of the People. And a stray dog sniffed at a pair of boots left behind in a plastic bivouac.
Meanwhile, government troops and tanks were gathering on roads leading to the zone. Manning a roadblock just outside the enclave, infantrymen seemed eager to push into what for three years was a rebel state within a state.
"We're just waiting for the president to send us in. The Army must recover the zone - it's our direct responsibility," said Corporal Rodrigo Rodriguez of the Hunters Battalion, which had been based in San Vicente del Caguán before talks began.
Also poised to enter the region are the illegal right-wing paramilitaries who are the Army's de facto allies in the war against the rebels.
Many locals fear that after living alongside the FARC for three years, they will be labeled by the paramilitaries as guerrilla collaborators and killed.
That fear is especially vivid for the members of the unarmed civil police force which worked with the FARC to ensure public order inside the enclave.
"We have no idea what will happen, but we know that we are in the sights of paramilitaries - we know that they'll take reprisals against us," said one civil policeman, who asked not to be named.
At San Vicente's one-story hospital, doctors and the International Red Cross are drawing up a contingency plan to deal with a possible outbreak of violence in the region. But the hospital is not prepared for a major crisis, said Dr Fener Villalba.
"The hospital isn't ready for a situation where the guerrillas, the army and the paramilitaries run into each other. In San Vicente, there have been three years with very little violence. But the moment the zone ends, there's going to be chaos," he said.
Staff writer Howard LaFranchi contributed to this report from Washington.