For the president’s many opponents, it was never just about derailing the peace deal.

As Colombia debated how to end 52 years of war with the nation’s largest rebel group, there was the soccer player from the beloved national team who condemned the agreement, singled out President Juan Manuel Santos and accused him of practices that were “not of God.”

Then there were the angry marches across Colombia this summer against a gay education minister, which soon grew into a wellspring of opposition to Mr. Santos’s government and the peace deal he was championing.

“My compatriots march in defense of family values,” declared Álvaro Uribe, the conservative former president who spearheaded the charge against the peace deal and rallied Colombia’s religious voters against it.

Mr. Santos’s push to end the war has earned him enormous recognition internationally, culminating in the Nobel Peace Prize on Friday. But he has faced stiff resistance in Colombia, where he is confronted by a growing cultural divide.