Afghanistan’s Hazara minority makes up 5 percent to 10 percent of the population. They have long been derided by other Afghans as outsiders because they are thought to be descendants of Genghis Khan’s Mongol invaders, who subjugated Afghanistan in the 13th century. Hazaras were long excluded from government jobs and education and once were mostly concentrated in the remote mountains of central Afghanistan, in an area known as Hazarajat.

But the Hazaras prospered after the American invasion, with many migrating to Kabul and sending their young people, including girls, to school in much greater numbers than any other group.

Much of Hazarajat escaped the warfare that has engulfed the rest of the country, which also helped the Hazaras to prosper. “In 13 years, there has never been one single Hazara suicide bomber,” Mr. Sahil said.

Often working or studying far from their Hazarajat homes, the Hazaras have had to travel long distances on dangerous roads to visit family members, making the recent attacks all the more disturbing for them. All of the attacks have been carried out against Hazara travelers, especially as they have passed through Pashtun areas where Taliban insurgents are prevalent.

That was what made the case of the 31 missing men so worrisome. The insurgents stopped three buses that passed within an hour on the country’s major highway, known as the ring road or Highway 1, as it runs through Zabul Province north of Kandahar.

The men’s abductors separated the Hazaras from Pashtuns and others, according to witnesses who were allowed to leave, and stuffed them into cars and drove them away. What most infuriated their families, however, were claims that the kidnappings took place on a stretch of highway between two government check posts that were so close that the security forces must have seen what was happening to the bus passengers.

“They said they couldn’t do anything to intervene because it was not their responsibility,” said Murtaza Farjad, 24, another Hazara activist in Kabul.