LAGOS, Nigeria (AP) — It has been nearly three years since Boko Haram extremists abducted almost 300 Chibok schoolgirls in northeastern Nigeria, shocking the world. Almost 200 of the girls remain captive. On Thursday, Nigeria’s army announced that soldiers had found one of the schoolgirls wandering in the bush near the Islamic extremist group’s forest stronghold. Here are some of the key events surrounding the crisis:

In this undated image taken from video distributed Sunday, Aug. 14, 2016, an alleged Boko Haram soldier standing in front of a group of girls alleged to be some of the 276 abducted Chibok schoolgirls held since April 2014, in an unknown location. Twenty-one of the Chibok schoolgirls kidnapped by Boko Haram Islamic extremists more than two years ago have been freed in negotiations, officials said Thursday, Oct. 13, 2016. Some 197 girls remain captive, though it is not known how many of them may have died. (Militant video/Site Institute via AP File)
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April 2014: Boko Haram extremists kidnap 276 schoolgirls from Chibok in northern Nigeria, the region where the insurgency emerged several years ago.
November 2014: Extremists seize Chibok, and Nigerian army takes back the town.
May 2015: New President Muhammadu Buhari is sworn in, pledging to tackle Boko Haram “head-on.”
April 13, 2016: Boko Haram video appears to show some of the Chibok girls, and tearful mothers recognize their daughters.
May 18, 2016: Relative says one of the Chibok girls is found, pregnant, in a forest; pressure grows on Nigeria’s government to rescue the others.
Aug. 14, 2016: Boko Haram video says some Chibok girls are killed in airstrikes and demands release of extremists in exchange for the other girls’ freedom.

In this photo released by the Nigeria State House, freed Chibok school girls sit during a meeting with Nigeria Vice President ,Yemi Osinbajo, in Abuja,, Nigeria, Thursday, Oct. 13, 2016. Twenty-one of the Chibok schoolgirls kidnapped by Boko Haram more than two years ago were freed Thursday in a swap for detained leaders of the Islamic extremist group — the first release since nearly 300 girls were taken captive in a case that provoked international outrage. (Sunday Aghaeze/Nigeria State House via AP)
Oct. 13, 2016: Spokesman for Nigeria’s president confirms 21 Chibok girls have been freed, a result of government negotiations with Boko Haram.
Nov. 5, 2016: Military announces the first army rescue of a Chibok girl, during a raid on a forest hideout.
Dec. 24, 2016: Nigeria’s president declares that Boko Haram has been crushed, driven from its last forest hideout.
Jan. 5, 2017: Nigeria’s army says soldiers find one of the schoolgirls wandering in the bush near the forest stronghold.