Ahead of Sunday's referendum on the government's peace deal with the Revolutionary Armed Forces of Colombia (FARC), a representative of the "yes" campaign had said there was no alternative for ending 52 years of armed conflict that have claimed about 220,000 lives. Now Colombian President Juan Manuel Santos needs a plan B.

The deal, finalized in June after four years of tortuous negotiations in Havana, was rejected by a tiny margin in a referendum on Sunday: Just over 50.2 percent of voters said "no," while just under 49.8 percent said "yes."

The result surprised both inside and outside observers - not least because recent polls had put the "yes" campaign ahead by as much as two-to-one. "It's probably very difficult now for Colombia to explain this to the rest of the world - what happened and why it happened," said Kristian Herbolzheimer, Colombia program director at the UK-based NGO Conciliation Resources.

A number of factors seem to have contributed to the shock: Analysts have pointed to Santos' lack of personal popularity and his decision to give so much prominence to FARC commander Timoleon Jimenez, aka "Timochenko," who has also lost much public support.

"FARC was never defeated militarily, but FARC definitely lost the public opinion campaign," Herbolzheimer said. This happened especially under the 2002-2010 tenure of Santos' predecessor, the right-wing Alvaro Uribe, who campaigned vigorously for "no," condemning the peace deal's amnesties for FARC guerrillas and raising fears that it would lead to a left-wing dictatorship.

Blaming FARC

It was during Uribe's presidency, Herbolzheimer said, that "the vast majority of Colombians started to see FARC as the main and only responsible party for the violence in Colombia, and that's deeply embedded and still there - no matter how strongly the government campaigned for peace and no matter how strongly the international support for peace is."

On top of this, many felt that the agreement simply left too many injustices unanswered. "Colombia is a completely traumatized society," Josefina Echavarria, a Colombian peace researcher at Innsbruck University, told DW. "There is so much anger, so much grief in the country. Many people feel like they're not being heard, and the government and all the groupings who supported the peace agreement clearly underestimated the size of this group."

The political consequences of the vote are now very unpredictable - Uribe has already called for Santos to resign - but all sides insist that the ceasefire is still in place and that negotiations will continue. "FARC reiterates its disposition to use only words as a weapon to build toward the future," Timochenko said after the result was announced. "To the Colombian people who dream of peace, count on us: Peace will triumph."

A better plan?

Given that both FARC and the government had previously insisted that this was the best possible deal, no one seems to be sure what will happen now. Herbolzheimer said the pressure was now on Uribe and the "no" campaign, rather than Santos and FARC.

"I think with the victory of the 'no' campaign comes a huge responsibility," he said. "I think the 'no' campaign has to come up with a plan B. What will most likely happen is that the peace talks will expand - the process will need to be reframed, leading to something more like multiparty talks. Clearly the 'no' campaign will have to participate in any further discussions."

But, even though no one wants to return to the battlefield, Sunday's result has obviously opened the risk of renewed violence. Among many new complications, no one is sure what will happen with the disarming of FARC - UN missions have already been deployed to supervise this process, which was scheduled to be completed in six months.

Can the rebels' solidarity survive this new stress test? For now, FARC remains "remarkably united," Herbolzheimer said - a fairly unique situation in the history of guerrilla conflicts around the world - but he agrees that the longer the new peace talks last, the greater the risk of this unity cracking.

The bigger danger, he argues, is from right-wing paramilitary groups, "who have a vested interest in keeping the status quo for their illegal activities and economies." "They can easily spoil the peace process by triggering violence and blaming FARC for it, and this can spiral out of control," he said.

Echavarria is a little more optimistic. "Thanks to the peace process, new initiatives have been founded in the past three, four years, which mainly work on a very regional, local level," she said. "Precisely because these movements are active in small villages, and work very specifically with families on the ground, I hope they will remain unaffected by this big national rejection of the peace agreement."