This confrontation is particularly acute in Dagestan. Here, Salafis, who believe in a return to the teachings of early leaders of the Muslim faith, face off against Sufis, who are supported by the official Spiritual Board of Muslims.
There is intolerance on both sides. In Makhachkala, the Dagestani capital, a Salafi woman dressed in a hijab and floor-length tunic showed me a recording on her cell phone of Sheikh Said-Afandi, one of the republic's most revered Sufi leaders.
"Disgusting," she said, as she watched scores of the sheikh's murids (followers) lining up to kiss his hands. "No man should make himself an intermediary between Allah and Muslims, demanding his own worship."
In the Islamist insurgents' online propaganda, where Sufis are condemned for "pagan practices" such as performing ritual dances and visiting the graves of their ancestors, the rhetoric gets even nastier. "Fed with a fatty broth, they are like a hoard of dirty pigs," says one diatribe. "They fawn before the [Russian] kafirs and are slaves of the butchers of the Kremlin!"
Yet such bile stems from a truth: Sufi leaders have been tainted by their ties with state officials and by their past readiness to marginalize Salafis, sometimes to the point of open persecution on the presumption that every Salafi is a potential terrorist. (The term Wahhabi -- often used for Salafis -- has become virtually synonymous with boyevik, a fundamentalist fighter.)
Although state-linked Islamic leaders in the North Caucasus rarely participate in this violence themselves, they have at times been willing accomplices. When militants assassinated Anas Pshikhachev, the mufti of Kabardino-Balkaria, on his doorstep in December, rebel sources said he'd been targeted for helping the police draw up lists of Wahhabis to interrogate, beat, and torture.
In Gubden, two Salafi men told me that they and other pious Muslims were regularly rounded up for questioning, purely on the basis of their beliefs. One said that his 77-year-old relative had been called a Wahhabi purely for saying that he didn't pray at the mosque, as some Salafis choose not to do.
His friend added: "So please show me, where in the Russian Constitution does it say that a man can be taken by police for not going to a mosque?
"They [security forces] do whatever they like, they burst into your home, they carry out searches without a warrant. There's no lawfulness; that's why we have this chaos in Dagestan. They put pressure on a peaceful man. It happens once, twice, three times. Finally he can't bear it anymore and goes to the forest [to join the boyeviki]."
Gubden has suffered immensely from these divisions, though you wouldn't know it at first. On the day I visited, people strolled along the village's narrow, winding streets. Two women in headscarves leaned over a wooden balcony to talk to a friend in the dust below, and a group of spindly cows drank from a stream.
But I hadn't been in town for an hour before I was detained. A group of plainclothes policemen, one carrying a Kalashnikov, came to the house where I was talking to three local men over tea and spoons of honeycomb.
The officers were jumpy. They took me to the station where Razdobudko's wife, Maria Khorosheva, had triggered her belt of explosives at the entrance (she too recorded a martyr video, saying her attack was retribution for Muslims being "killed and tortured" in Russia). The building was surrounded by high walls, barbed wire, and rows of concrete barriers designed to stop vehicles approaching.
I was questioned for almost two hours, as were the men with whom I'd been talking. The senior officer at the station, on the basis of no evidence, suggested I had forged links with militants in the village.
I got used to such accusations during my journey. Senior officials in Russia regularly say -- without providing proof -- that the CIA and other foreign spy agencies fund Islamists in the Caucasus. Any Westerner passing through the region is seen as a possible go-between.
I also understood why the police felt nervous. On the wall of the room where we sat was a portrait of a square-jawed man with steel-gray hair in a uniform and a peaked cap. I recognized the face. It was Abdulmalik Magomedov, the former chief of the Gubden police.
Magomedov was shot dead in a skirmish with fighters near the village in 2008. A year later, his wife, daughter, and older sister would die in one of the cruelest acts ever committed by the militants. The three women had gone to Magomedov's grave in one of Gubden's cemeteries on the anniversary of his death. As they began to read passages from the Quran, a bomb laid by the grave exploded, killing them all. Last summer, Magomedov's surviving son, Ruslan, was assassinated in the middle of the village. The entire family, now, is gone.
And so the policemen crouch in their fortress, radiating fear and hatred. "We don't go out in uniform," explained one, called Umar. "It's too dangerous." Another said with disgust: "One day the Wahhabis plead they are peaceful, repressed believers, and the next they'll drag you off and kill you, or hold you for ransom."