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The effort to extinguish the UP was carried out by a brutal chimera of state security forces, armed right-wing groups, and drug traffickers — most prominently members of Pablo Escobar's Medellin cartel.

Leftist rebel groups had stolen from the cartels and kidnapped members of drug traffickers' families in the early 1980s, prompting the capos to form their own paramilitary groups.

The newly enriched drug traffickers were also motivated by what they saw as a threat posed by the UP and the ascendent political left to their growing economic interests, particularly their control of land that had often been taken by force from civilians.

“There is a direct relationship between the emergence, activity and the electoral support of the Patriotic Union and the killing of its activists in regions where the presence of that party was interpreted as a threat to the maintenance of the privileges of certain groups,” a 1992 report by the Colombian ombudsperson noted.

(Rebels of the Revolutionary Armed Forces of Colombia, FARC, attend the inauguration of their 10th conference in Yari Plains, southern Colombia, September 17, 2016.AP Photo/Ricardo Mazalan)

These interests aligned drug traffickers with Colombia's elite social classes, who for economic and political reasons also wanted to combat the left-wing guerrillas, a desire that overlapped with the strong anti-communist bent of the Colombia's leaders and the US government at the time.

For the US's part, officials, including the then-US ambassador to Colombia, charged that leftist guerrillas had been cooperating with traffickers, making them "narco-guerrillas," though the extent of their cooperation at the time has been questioned. The US government took a staunchly antidrug stance, even if it had proven willing to overlook trafficking for political reasons, particularly if those doing the trafficking were aligned against communism.

The Reagan administration, according to Grandin, "provided no support for the peace process and no shelter for leftists who were trying to lay down arms and commit to electoral politics."

Members of the nascent UP Party were thus targeted by members of paramilitary groups and other rivals in a violent campaign in which the Colombian government was often complicit.

(Colombia's former president, Alvaro Uribe, speaks to the media after casting his vote in Bogota, June 15, 2014.REUTERS/Jose Miguel Gomez)

The bloodshed proved their success, and as a consequence, the FARC (which continued to grow during the UP's rise) returned to the scene as a rebel group in the 1990s, eventually assuming a larger role in the drug trade as the cartels broke up in the later part of that decade.

The FARC's power was greatly diminished by a US-backed, Colombian-led offensive in the 2000s (led by then-President Alvaro Uribe, who opposes the current peace deal).

And the UP, which lost official recognition as a party in 2002, had its legal status returned in 2013, though now it sees itself as a leftist party, rather than socialist or communist one.

Yes vs. No

In the current environment, there are still some unpleasant reminders for FARC rebels and those linked to them of the dark days in the late 1980s.

The paramilitary groups that hunted UP members kept at it through the 1990s, eventually becoming full-fledged criminal groups. Those paramilitaries disarmed in the mid-2000s — and thousands of former paramilitaries were killed after that demobilization as well — but during and after that they forged ties to Colombian politicians, expanding their roles in organized crime. In recent years, hundreds of public officials have been arrested for ties to criminal bands descended from paramilitaries.

Santos, the current president, has made assurances that right-wing groups and their criminal descendants will not have the same power they did after the FARC's earlier attempt to enter political life.

(A group of Self-Defense of Cauca paramilitaries walk as two girls look on in the rural area of Cajibio, Colombia, in the southern Cauca state, November 28, 2003.AP Photo)

"The lion's share of our armed forces, soldiers and police, have been concentrated in the war against FARC ... we've decided not to reduce our army or our police — on the contrary we're strengthening it more, and all of these people will be concentrated in fighting these criminal bands, and they know that," Santos said at a Reuters event in New York City this week.

"Only this year, we have captured or killed more than three-and-a-half-thousand members of these criminal bands; we have seized more cocaine than ever before, so we're just starting to do that, so they know that the future is not very bright," he added.

But the Colombian government has a poor track record when it comes to protecting demobilized combatants. And while the military is better trained, the rule of law has improved, ex-paramilitary leaders themselves have given their support to the peace process, and international support will be available for the demobilization, signs of potential blowback against demobilized FARC members remain.

(FARC rebel leader Rodrigo Londono, better known by nom de guerre Timochenko, center, and other leaders sing the anthem at the camp where they are preparing for ratifying a peace deal with the Colombian government, near El Diamante in Yari Plains.Thomson Reuters)

The fervent "No" campaign against the peace deal, led by former President Uribe — who has been linked to paramilitary groups — appears to have led to violence against peace-deal supporters.

In the three weeks after the Colombian government and FARC rebels announced their cease-fire, 13 activists promoting peace were killed, according to Colombia Reports. Dozens of others have gotten death threats and at least one man has fled his city for the safety of the capital.

"What is concerning is that in the majority of cases they were killed presumably for reasons related to the promotion of 'Yes,'" the Electoral Observation Mission, a civil-society group, said in a report about irregularities related to the vote.

Many of those killings took place near places where FARC rebels are to gather to demobilize. And while those areas are to have buffer zones as well as have a security presence, such killings raise the specter of more attacks on rebels who are once again out in the open.

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