No one knows how many children have been affected by the spread of Boko Haram across Nigeria and neighboring countries. This photo shows the school uniforms of the girls kidnapped from a school a year ago. Glenna Gordon/Glenna Gordon for NPR hide caption

itoggle caption Glenna Gordon/Glenna Gordon for NPR

Nigerian electoral officials collate results at a polling station in the oil rich Niger Delta, Port Harcourt, Nigeria on Sunday. Millions of voters headed to the polls in the Nigerian general elections after being delayed for over a month. Tife Owolabi/EPA/Landov hide caption

itoggle caption Tife Owolabi/EPA/Landov

Nigeria's President Goodluck Jonathan, left, and opposition candidate Gen. Muhammadu Buhari, right, prepare to sign a renewal of their pledge to hold peaceful "free, fair, and credible" elections, at a hotel in the capital Abuja, Nigeria, on Thursday. Ben Curtis/AP hide caption

itoggle caption Ben Curtis/AP

Nigerian President Goodluck Jonathan speaks during the inauguration ceremony of the 750 megawatt power station in the southwestern Ogun state, Nigeria, last month. In an interview with the BBC Friday, he said he hopes to retake all territory seized by Boko Haram within a month. Jiang Xintong/Xinhua/Landov hide caption

itoggle caption Jiang Xintong/Xinhua/Landov

The most recent propaganda videos from Boko Haram have higher production values than in the past and other similarities to ISIS-produced videos. Boko Haram/Sendvid hide caption

itoggle caption Boko Haram/Sendvid

An armored vehicle used by Boko Haram militants captured by the Nigerian military in Maiduguri, Borno state, late last month. The extremist group appears to be expanding its operations into neighboring countries in an effort to establish an independent Islamic state. EPA/Landov hide caption

itoggle caption EPA/Landov

An official stands in front of relief materials at a camp for displaced people in Maiduguri in Borno State last week. The town, where many have gathered after fleeing Boko Haram attacks, is now said to be under assault from the Islamist extremist group. Reuters/Landov hide caption

itoggle caption Reuters/Landov

Comedian Trevor Noah was born in South Africa during apartheid — "born a crime," as he says. Byron Keulemans hide caption

itoggle caption Byron Keulemans

Satellite image of dense housing in Doro Baga taken on Jan. 7, following an attack by Boko Haram. This shows almost all the structures razed. The inset demonstrates the level of destruction of most of the structures in the town. The red areas indicate the remaining healthy vegetation. Micah Farfour/DigitalGlobe hide caption

itoggle caption Micah Farfour/DigitalGlobe

A group of Nigerian traditional hunters and vigilantes gather on vehicles on their way to engage Boko Haram militants in Mubi from Yola, Adamawa State, in November. The hunters have being assisting the Nigerian military in their fight against the Islamic insurgents. STR/EPA/Landov hide caption

itoggle caption STR/EPA/Landov

Maureen B. Kabrik, a "#Bring Back Our Girls" campaigner, speaks during a sit-out meeting in Borno in support of the release of more than 200 Nigerian schoolgirls in August. Boko Haram militants, who seized the girls last April, have reportedly captured a key military base in the region. Afolabi Sotunde/Reuters/Landov hide caption

itoggle caption Afolabi Sotunde/Reuters/Landov

Members of the Abuja "Bring Back Our Girls" protest group sit during a march in continuation of the Global October movement. Once again, Boko Haram militants are implicated in killings and mass kidnapping in northeastern Nigeria. Afolabi Sotunde/Reuters/Landov hide caption

itoggle caption Afolabi Sotunde/Reuters/Landov

Civilians who had just recently arrived in Yola prepare to flee again, this time in a large open-top truck headed to the city of Jos. Ofeibea Quist-Arcton/NPR hide caption

itoggle caption Ofeibea Quist-Arcton/NPR

#BringBackOurGirls" campaigners participate in a lamentation parade in Abuja, in early November, as more towns in Nigeria come under attack from Boko Haram. Afolabi Sotunde/Reuters/Landov hide caption

itoggle caption Afolabi Sotunde/Reuters/Landov

Ramatu Usman, shown here with one of her sons, is a 37-year-old mother of eight. She says she was separated from one of her sons, 6-year-old Yahaya Buba, following an attack. He is still missing. Ofeibea Quist-Arcton/NPR hide caption

itoggle caption Ofeibea Quist-Arcton/NPR

People inspect the site of a suicide bomb explosion at the Government Science Technical College in Potiskum, Nigeria, Monday. Survivors say a bomber disguised in a school uniform detonated explosives during an assembly at the school. Adamu Adamu/AP hide caption

itoggle caption Adamu Adamu/AP

People call for the Nigerian government to rescue girls taken from a secondary school in Chibok region, during a protest earlier this month. Boko Haram, the group that took the girls, says they have been "married off." Olamikan Gbemiga/AP hide caption

itoggle caption Olamikan Gbemiga/AP