The fate of 219 Chibok schoolgirls remains unknown after Boko Haram militants kidnapped them from a middle school in Borno State, Nigeria in 2014.
More than 200 girls have been held captive by one of the world's deadliest armed groups for over two years.
The abduction drew international attention when the #BringBackOurGirls Twitter campaign sparked global outrage on social media. Millions of people around the world, including celebrities, took part in the campaign and showed solidarity with the families of the victims.
But the fate of the Chibok girls remains the biggest challenge that Nigeria faces. According to The New York Times, the government has attempted to negotiate several times. Each effort was unsuccessful.
How did Boko Haram kidnap the girls?
On April 14, 2014, Boko Haram militants launched an attack on a state-run boarding school in Chibok, a town in Nigeria's Borno State.
That night, militants raided the dormitories and 276 schoolgirls were forced into vans by Boko Haram militants. Some of the students managed to escape immediately after their abduction, but 219 girls are still missing.
What is Boko Haram?
Jama'atu Ahlis Sunnah Lidda'a Wati Wal Jihad, better known by the more colloquial Hausa language term Boko Haram, opposes "Western-style education" taught in public schools in Nigeria.
Boko Haram translates to "Western education is forbidden", an idea which originated from the teachings of a Nigerian cleric, Muhammad Yusuf, who became known in the 1990s. He also called for the removal of any form of secular authority.
Eventually, things came to a head in 2009 when a clash between his followers and the police led to a bloody showdown between the group and the government which lasted several days.
The DAESH-affiliated group continues to devastate the lives of millions of people in northern Nigeria and the entire Lake Chad region.
Since 2009, the group has killed over 15,000 people and displaced more than 2 million others.
The most brutal massacre perpetrated by Boko Haram to date took place in the north-eastern town of Baga, which is home to 300,000 residents. The multi-day attack left at least 2,000 dead.
The militant group has also used children as sex slaves and suicide bombers.
Over the past three years, the group has kidnapped more than 10,000 boys and trained them in camps in abandoned villages and forests, according to government officials in Nigeria, its neighbouring country Cameroon, and the Human Rights Watch, a New York-based advocacy group.
As of May 2016, the militant group has used 113 females as suicide bombers according to The Long War Journal.
What has been done to combat Boko Haram?
President Muhammadu Buhari came to power in 2015. Buhari has made the fight against terrorism a top priority for his administration and has vowed to defeat the militants. However, he faces much criticism for not securing the release of the kidnapped schoolgirls.
Last July, a regional force was created with troops from Lake Chad countries: Nigeria, Chad, Cameroon, Niger and Benin. The force managed to push Boko Haram and associated militant groups out of towns they had previously captured.
In addition, the US, United Kingdom, France, China and Israel have also provided military and intelligence support to the Nigerian Army.
When Boko Haram first emerged, the group successfully exploited public anger and frustration over corruption, poverty and political marginalisation of northern Nigeria by the federal government.
Critics say military solutions will not work unless the Nigerian government reduces poverty and builds a strong education system in north-eastern Nigeria.
What has Nigeria done to get the girls back?
Former president Goodluck Jonathan has been criticised for reacting to the kidnapping two weeks after it took place. In March 2015, the governor of Borno State, Kashim Shettima, said Jonathan called him 19 days after the kidnapping.
Negotiations began in July 2015 between the Nigerian government and Boko Haram to gain the release of the girls, according to Nigerian officials.
The talks began soon after President Muhammadu Buhari took office but were derailed.
The government said Boko Haram demanded the release of prisoners involved in "major terrorist actions" and others who were explosives experts. Buhari agreed to these orders, no matter how difficult they were, according to the government statement, "believing that the overall release of these girls remains paramount and sacrosanct."
Yet, none of these attempts have been successful.
Last week, the president asked the UN to help mediate with the militant group during a bilateral meeting with Secretary General Ban-ki Moon in New York.
"The split in the insurgent group is not helping matters. Government had reached out, ready to negotiate, but it became difficult to identify credible leaders. We will welcome intermediaries such as UN outfits, to step in," Buhari said.
Author: Mucahid Durmaz