It could not have been closer: by a margin of 0.4% the people of Colombia have rejected a peace agreement that would have brought a formal end to 52 years of civil war and allowed the remaining 7,000 fighters of the Fuerzas Armadas Revolucionarias de Colombia (Farc) to reintegrate into the nation’s life and politics. With their votes, Colombians have highlighted the country’s profound geographic and political divisions and left Colombia, once again, on the edge of the unknown.

What President Juan Manuel Santos presented to the voters as a historic opportunity has turned into a political nightmare. It was a deal supported by everyone from Barack Obama to Pope Francis – although the conservative church leaders in Colombia had maintained a notable silence on the subject. Perhaps reassured by polls that predicted a comfortable win, the president’s administration, as one insider remarked last week, had no Plan B.

Why did a fraction more than half the voters, in a country blighted for the entire lives of most of its citizens by a war that has killed 250,000 people and displaced 6 million, reject the offer of peace and the investment and prosperity that it might bring?

Colombia’s long history of violence and its tortured politics offer many possible explanations: Santos is not personally popular and by putting himself and the Farc commander-in-chief Timoleón Jiménez – Timochenko – front and centre of the agreement, and the lavish signing ceremony organised a week before the referendum, he alienated as many voters as he attracted. “If he had had the grace to step back and let the victims speak,” complained one Colombian commentator before the vote, “it would have been completely different. He would have held the moral high ground and people could have voted for peace without feeling they were being invited to support Santos.”

Álvaro Uribe argued that, once the ex-guerrillas entered politics, Colombia would end up with a leftwing dictatorship

Repeated hints from supporters of the president that he and Timochenko were in line for a Nobel peace prize did not help. Why should a guerrilla leader with so much blood on his hands, people complained, be honoured with such a prize?

Colombia’s former President Uribe during a protest against the government’s peace accord with the Farc. Photograph: John Vizcaíno/Reuters

The far-right former president Álvaro Uribe, who retains strong support in his home base of Antioquia, campaigned vigorously for “no” for reasons of ideology as well as self-interest. Under Uribe’s presidency, killing by the army and far-right militias escalated to new heights, as did the land grabs that fuelled much of the violence in that phase of the war. A national survey last year confirmed that nearly half of Colombia’s land is owned by 0.4% of the population, and even had the agreement passed, few of those who gained land through paramilitary violence were ready to hand it back.

In the days before the referendum, prospective voters in Medellín – a stronghold of Uribe’s – offered a range of reasons to vote no: that the Farc would be allowed to keep their ill-gotten gains; that once the ex-guerrillas entered politics, Colombia would end up with a leftwing dictatorship; that ordinary Colombians would have to pay for the deal while the men of violence reaped the gains of the peace; and finally that those with blood on their hands would not be punished for past crimes.

Other less polarising figures, such as the conservative former president Andrés Pastrana, also supported a no vote, arguing that the agreement conceded too much to the Farc. Santos was wrong, he said, to frame it as a choice between peace and war: in this political argument, all sides claim to want peace. But for Pastrana, the choice was between this deal and a better one that he believed was possible. The Farc themselves, Pastrana insisted, had said that they would not return to arms in the event of a no vote.

It remains to be seen whether the Farc will finally put down their guns and accept less favourable terms: Colombia’s capacity for violence of both the far left and the far right is undiminished, and Timochenko’s authority has been shaken by this shock result, as has Santos’s: Uribe’s party lost no time in calling for the president to step down.

In the minutes that followed the announcement of the final result, Timochenko promised on Twitter that he would continue to talk, and the Farc tweeted that: “The love we feel in our hearts is gigantic and with our words and actions will be able to reach peace.”

Few Colombians will have been moved by this declaration of love from a movement with the Farc’s record of kidnapping and violence, despite some recent expressions of regret for the suffering of the victims. And infinite love aside, it would be no surprise if many of the Farc rank and file were to reach nervously for their weapons and return to their bases.

When a sober President Santos emerged to make a statement, three hours after the polls closed, he too insisted that the ceasefire remained in place and announced that he would convene all sides in the political argument to discuss a way forward. He went on to guarantee national stability, public order and the continued search for peace. Colombians on all sides of this bitter conflict have need of all three.