This is the story of what comes after the headlines. What happens after the shock dissolves and the news marches onto the next tragedy. This is what happens to the boys, girls and women who are kidnapped by Boko Haram — and why.

Every few months, another fresh kidnapping grips northeastern Nigeria, where the Islamic militants are embroiled in several campaigns against the forces of Nigeria, Chad and Niger. The most — and perhaps only — famous kidnapping is, of course, what occurred around this time last year at a school in the city of Chibok. There, Boko Haram made off with hundreds of schoolgirls and did god knows what with them. They were said to have become “sex slaves,” married off to any number of militants, and haven’t been heard from since.

But there have been many more kidnappings than that. Tuesday brought fresh evidence. According to the BBC and Reuters, hundreds of women and children have been reported missing in a the town of Damasak, which was just reportedly liberated from Boko Haram’s yoke. Specifics are sketchy. Reports don’t agree on either the number of people taken, nor whether the missing are exclusively children under the age of 11 or include women as well. “They took 506 young women and children” in Damasak, a trader named Souleymane Ali told Reuters inside the town. “We don’t know if they killed others after leaving, but they took the rest with them.”

Ali’s own wife and three daughters were taken as the Boko Haram militants fled. “Two of them were supposed to get married this year,” he said. But Boko Haram “said, ‘They are slaves so we’re taking them because they belong to us.’ ”

Mass kidnapping of women and children has come to define the barbarity of Boko Haram. But it’s actually a fairly recent development in its 14-year history — and can in part explain the horrifying rise of a terrorist organization that this month pledged allegiance to the Islamic State. To be sure, Boko Haram has always kidnapped. But as the operation has become more sophisticated and sprawling and in need of additional human capital, Boko Haram has widened its efforts from capturing foreigners — who can be ransomed off for big bucks — to targeting mass numbers of young women and children who can be put to other uses.

Before, Boko Haram’s terrorism tactics were relatively rudimentary, though effective. Drive-by assassinations. Setting fire to churches and schools. These assaults “required minimal training,” noted Jacob Zenn of West Point’s Combating Terrorism Center. That began to change in late 2010 and 2011 with sophisticated bombing strikes. Then in 2013, the kidnapping opened in earnest, rising to international notice with the capture of 250 girls taken from Chibook. Zenn called this mass kidnapping on April 14 a “turning point.”

Consider what happened next, according to Zenn. “On April 19, May 5, June 10, 2014, the militants took more than 40 girls from the towns near Chibok, and on October 20, 2014, took 45 more girls from Wagga, Adamawa State and ‘married’ the young ones. … [It is] estimated that Boko Haram may have abducted between 500 and 2,000 women since 2013, but most incidents go unreported.”

Mass kidnappings have become essential to Boko Haram’s campaign. The kidnapped are used as soldiers. They’re used as wives. They’re used as bargaining chips. They’re used as cooks, as suicide bombers and as future soldiers. Boko Haram, unlike the Islamic State, doesn’t worry about attracting fresh recruits. They simply take them. It’s an effective method of swelling their ranks to match the international coalition assembled to fight them.

“These gunmen had been telling us to join them to fight our soldiers here and at the borders with Cameroon and Chad,” one boy told the Nigerian publication Vanguard last September. “… The insurgents were adamant and ruthless threatening us to either be conscripted and fight against the troops in Gamboru or be killed.” He added: “Since last Monday’s attacks, these sect boys have been going from house to house in search of residents in hiding. … Residents who refused to join the insurgents were summarily executed using guns or knives and swords.”

Yet the kidnapped and conscripted appear expendable for Boko Haram. In the past few months, a rash of disturbing news has risen out of northeastern Nigeria telling of very young girls used as suicide bombers. In January, for example, a girl said to be as young as 10 was strapped with explosives. She marched into a market, where the bomb exploded, killing at least 16 people.

“Only after the Chibok kidnapping did Boko Haram start using women in operations,” Zenn wrote, citing an apparent “operation link between the kidnapping in Chibok and the deployment of the female suicide bombers, even though the schoolgirls were likely not the bombers.”

“Using children to carry and detonate explosives is not a new tactic for Boko Haram, but it is an intensification,” Elizabeth Donnelly, assistant head of Chatham House’s Africa program in London, told NBC. “Boko Haram has been abducting and conscripting children and young men and women for a long period for various purposes. They will be seen by the movement as expendable resources.”

Last week, Agence France-Presse and other news organizations reported that “dozens of Nigerian women who were forced to marry Boko Haram fighters were slaughtered by their ‘husbands’ before a battle with troops” in the northeast town of Bama. Witnesses told AFP  that “they killed the women to prevent them from subsequently marrying soldiers or other so-called non-believers. … ‘The terrorists said they will not allow their wives to be married to infidels,’ said Sharifatu Bakura, 39, a mother of three.”

No one knows what will happen to the 500 children said on Tuesday to be taken by Boko Haram. But the rationale behind their capture seems all but certain to local experts. “The very young ones, they will give to the madrassas,” Borno state Senator Maina Maaji Lawan told the BBC,” referring to Islamic religious schools. “And the male ones between 16 and 25, they conscript them and they indoctrinate them as supply channels for their horrible missions.”