Peace talks between the Colombian government and Marxist rebels from the Revolutionary Armed Forces of Colombia, or Farc, are due to resume in the Cuban capital, Havana. But it is the thorny issue of land ownership that could make or break the negotiations aimed at ending Latin America's longest-running insurgency. Colombia's hopelessly unequal tenure of farmland was the reason the Farc first took up arms in the 1960s, as millions of desperate peasants, guided by Marxist ideologues, finally decided they had had enough of a powerful post-colonial élite whose ranches covered vast stretches of the national territory.

When the conflict started, just 3 per cent of landowners held more than half of Colombia's farmland. Yet after half a century of fighting, 250,000 dead and millions more displaced, the problem has only deepened. In 2005, just over 16,000 individuals – roughly 0.4 per cent of all Colombia's landowners – controlled 63 per cent of the land. Meanwhile, 3.3 million subsistence and peasant farmers, mainly Afro-Colombians or of indigenous descent, eked out a living on less than 9 per cent of the land.

The conflict itself forced many to flee their homes. And drug barons and far-right militias funded by rich ranchers also jumped at the chance created by the lawlessness in remote rural areas to threaten smallholders into handing over their plots of land. Experts believe that between 5.4 million and 13.6 million acres were illegally seized in this way.

Even Juan Manuel Santos, Colombia's centre-right President, agrees that the country needs reform of land ownership. Yet the two sides appear as divided as ever over the form it should take. "Agrarian reform is not a simple mathematical redistribution of lands, but the result of a state of social equality and justice, of the deeply desired good life for all the residents of the countryside, the return to the values of collectivism and community," a member of the Farc's national secretariat, Pablo Catatumbo, wrote on one of the rebels' websites after the first round of talks in Oslo last month. But that idyllic view could not contrast more starkly with the reality of a terrorist organisation demanding an end to "capitalism" at the point of a gun. Funding itself through kidnapping and cocaine-trafficking, the Farc has frequently murdered the rural poor it claims to represent.

Yet although the Havana talks will, by mutual agreement, focus on "comprehensive agrarian development", the government's negotiators have stated emphatically that they will not stray from that narrowly defined "pragmatic" order of business.

"For that [the economic model] to be discussed as part of the Colombian agenda, the Farc must lay down its arms, enter politics and win elections, but at this point it is not on the agenda," said the government's chief negotiator, Humberto de la Calle, a former Vice-President, as the Oslo round concluded. Nevertheless, his boss Mr Santos has moved a long way from the stance of Alvaro Uribe, his hard-right predecessor, in addressing the deep inequalities that run through Colombian society, including a recent law to return stolen land to its original owners.

This has infuriated Mr Uribe, who has turned against his former defence minister for allegedly giving the Farc political and military oxygen. But while Mr Uribe, whose father was killed by the Farc in a botched 1983 kidnapping, insists that the only way to stop the group is by force, Mr Santos believes he has spotted a historic opportunity to negotiate peace from a position of government strength.

The Farc is currently thought to have some 9,000 combatants, half their number a decade ago, after years of successful counter-insurgency operations by the Colombian army. Crucially, the President has refused to call a ceasefire until the talks conclude to his satisfaction – and the Farc has continued its attacks, killing soldiers and torching vehicles in breach of the curfew it has imposed in remote jungle provinces.

Yet should the negotiators reach agreement on land reform, there then awaits a long list of other sensitive issues, including the fate of the estimated 500 outstanding kidnap victims –whose existence the Farc denies – amnesties for the rebels, and the reintegration into civilian life of guerrillas used to life on the run and armed to the teeth in Colombia's dense jungles. And as Mr Santos proceeds, he is being watched hawk-like by the Farc's many victims.

"As the relatives of victims, we need to be informed about what exactly the government is prepared to put on the table, and what it won't negotiate," said Ismael Marquez, president of the National Association of the Kidnapped and Disappeared, whose 30-year-old son, a lawyer, has been missing since his kidnapping in 1999. "Unless you have lived what we are going through, without knowing the fate of our son, it is impossible to understand," he said.

Nevertheless, there is a growing sense of cautious optimism among war-weary Colombians. But before they get their hopes up further, negotiators will have to find a way to slice through the Gordian knot of land reform.

A history of violence

May 1964 Revolutionary Armed Forces of Colombia (Farc) are established by survivors of a government crackdown on a Communist-inspired peasant group.

June 1975 A nationwide "state of siege" is imposed amid heightened violence between left-wing rebels and government troops.

March 1984 The Farc agrees to start negotiations with the government of President Belisario Betancur.

February 2002 Following high-profile Farc abductions, government sends troops into south-east.

August 2002 Alvaro Uribe takes power, promising to crush the Farc.

October 2012 Peace talks are formally launched in Hurdal, a small town in Norway.