MORROA, Colombia — Caught in the crossfire between far-right militias and leftist rebels, 40 families abandoned the farm they shared in the foothills of Colombia's Montes de Maria range. The land repeatedly switched hands before being sold to a businessman.

Nearly a decade later, a court in April returned the 770-acre (310-hectare) farm, called Pechilin, to the families without paying the businessman a penny. But none have gone back to raise cattle and cultivate cassava, corn and tobacco.

"Who is going to guarantee our security?" says Donaldo Ruiz, a tall, burly 54-year-old who does not look like the sort of man who scares easily.

Illegal armed groups believed to be largely in the hire of owners of ill-gotten land are threatening a bold, unprecedented effort by President Juan Manuel Santos' government to return vast expanses of land stolen from poor farmers. They've assassinated at least 55 land reform activists since 2008, human rights groups say.

Santos' land restitution campaign is considered central to peace talks being held in Cuba with Colombia's main leftist rebel group, the Revolutionary Armed Forces of Colombia, known as the FARC. It addresses their central demand for a radical agrarian reform that fundamentally changes Colombia's countryside, so a failure by the government to return the land could undermine what many consider the best shot ever at ending Colombia's half-century-long internal conflict.

Tens of thousands of parcels across rural Colombia, equal in size to the U.S. state of New Jersey by conservative estimates, were stolen by illegal armed groups or abandoned over the past quarter century, often with the collusion of corrupt local authorities or judges.

After Santos took office in 2010, he made returning the land to its rightful owners a hallmark of his presidency.

Pedro Geney, a land reform activist in the regional capital of Sincelejo, said criminal gangs that grew out of the far-right militias known as paramilitaries have created "an anti-restitution army" to resist the return of the lands.

"We are waiting for (the government) to tell us what the security model will be, because it certainly can't be a car and two bodyguards for each person who returns," Geney said.

The killers' latest confirmed victim: Ivan Dario Restrepo, a 44-year-old activist slain May 4 in his home in Bello, Antioquia, also in Colombia's northwest.

Since the paramilitaries emerged in the 1980s, Colombia's land has become concentrated in fewer hands. Drug traffickers laundered profits by buying up vast cattle ranches, and agribusinesses thrived often through shady dealings and land theft.

According to the government, 60 percent of the country's arable land was in the hands of just 14,000 owners in 2011, while 2.5 million families held less than 20 percent.

Colombia's peace commissioner, Sergio Jaramillo, told The Associated Press that authorities can reverse the concentration by "taking some of the best land in the country from those who acquired it illegally and distributing it to those who need it."

On May 26, in Cuba, negotiators from the government and the FARC reached a 20-page agreement, whose details are confidential.

Jaramillo, however, said the agreement is "very precise" about what happens in the countryside if a final peace pact is reached and the estimated 8,000 FARC fighters put down their weapons.

Farmers will get land titles, bank loans, technical assistance, help with irrigation systems and road and school improvements, and the government will conduct a complete inventory of rural lands to ferret out fraud, Jaramillo said. A property tax plan also will be imposed to discourage land from lying fallow, he said. Land reform has always been the peasant-based FARC's central demand.

Jaramillo added that after a peace treaty, the criminals who murder land restitution campaigners will no longer enjoy near impunity because the forces of law and order will have new allies: demobilized FARC fighters and some sort of international supervision.

But negotiators on both sides have made clear that nothing in the peace pact will be agreed upon until the whole deal is finalized, meaning the land deal depends on the signing of the peace pact.

Negotiators resumed talks last week focusing on the issue of rebel leaders' participation in politics. Later on the agenda: weaning the rebels off cocaine trafficking as a funding source.

On land reform, the challenges remain immense.

An estimated 5.7 million people in Colombia have been forced from their homes over the past quarter century, according to CODHES, a non-governmental group that tracks them. The country has long been home to the Western Hemisphere's highest number of internally displaced people.

Land expert Yamile Salinas of the non-governmental group Indepaz says less than half of 1 percent of the estimated 7,800 square miles (2 million hectares) that the government says was stolen or cleared have been ordered returned by court rulings over the past two years. In those rulings, 57 percent of the dispossessions were blamed on paramilitaries.

According to the Agriculture Ministry, of the 35,846 requests it has received nationwide for land restitution, at least one in three is blamed on the rebels, although FARC leaders have vehemently denied stealing land. Another third were blamed on paramilitaries, the rest on unspecified criminal bands.

The government says the FARC stole huge expanses from the state, mostly in remote regions where it held sway.

In Sucre state where Pechilin sits, the thieves were overwhelmingly paramilitaries, and just 20 of more than 1,650 restitution requests have been addressed, officials say.

The Montes de Maria region has long been a key corridor for cocaine traffickers smuggling the U.S.-bound drug by boat along the Gulf of Morrosquillo on Colombia's northern coast near Panama.

Ranchers and drug traffickers first formed the paramilitaries in the 1980s to counter rebel kidnapping and extortion. The Montes de Maria region bore Colombia's most horrific bloodletting from 1996-2001 as far-right militias turned on civilians they suspected of being rebel sympathizers while, along with the military, they tried to expel FARC from the region.

In all, illegal right-wing militias killed 354 people in 42 massacres, according to the Center for Historical Memory, a state-funded public archives project.

Pechilin was caught in the crossfire, and most of its residents fled to Morroa, a nearby town of unpaved red-clay streets and mud-wall homes with intermittent electricity and water services.

Nellis Payares and her mother, Doris, shuddered at the thought of returning to Pechilin, even though they would qualify for government credits to rebuild and replant there.

"After what happened there, it's tough," said Payares, 21.

Her 68-year-old father, Luis, was hacked to death with machetes in September 2005 while trying to prevent the theft of his cows. No one ever determined the killers' identities.

Payares, her mother and her seven siblings had by then already fled the farm. She said she remembered diving under a bed as a child when gunfire broke out nearby.

A smile brightened Payares' face, though, when she imagined buying 10 cows and having them roam the old farm with her children. Her family was cooped up in her mother's cluster of three dirt-floor shacks in Morroa, which have no running water nor electricity.

None of Pechilin's 40 families have moved back to Pechilin even though all have deeds to their pieces of the farm.

"We are not going to fix this overnight," said Elina Rivero, a top official in the state land restitution office. "It's not that easy to erase the truly tragic history these families may have lived."