Hari Sreenivasan:

Boko Haram has cut an infamous and deadly reputation for itself in Nigeria.

And a particularly cruel tactic of the Islamist militant group is every parent's worst fear: the kidnapping and killing of children.

In a moment, you will hear testimonials from two young women who survived that experience, but first some background on the group and the fight against it.

Boko Haram's near-decade-long campaign of terror and violence has killed tens of thousands and displaced two million people. Their main focus, to overthrow Nigeria's government and establish an Islamic state that forbids Western-style political and social activity.

Boko Haram translates to Western Education is Forbidden. The group has carried out attacks in Cameroon, Niger and Chad, all from its base in remote Northeastern Nigeria.

Since 2009, the militants have terrorized Africa's most populous country with bombings, assassinations and abductions. Just last month, an ISIS-affiliated faction of Boko Haram kidnapped 110 girls from a boarding school in Northeast Nigeria, some as young as 11 years old.

Last week, the Nigerian government shuttered boarding schools in the northeastern state and sent drones and jets to search for the girls. Boko Haram often marries the captives off to fighters. They have also been used as suicide bombers.

In 2014, the militants abducted nearly 300 students from a school in the village of Chibok, prompting an international campaign to free them. More than 50 girls escaped. About 100 more were freed last year, after the Nigerian government paid a nearly $4 million ransom. Some had been forced to convert to Islam and sold as sex slaves. They were beaten, starved and sexually assaulted.

Recently, Judy Woodruff sat down with two young women who were abducted in 2014 and escaped.

Ya Kaka was 15 when taken, Hauwa, 14. They were brought to the U.S. by a nonprofit called Too Young to Wed dedicated to protecting young girls and ending child marriage.