People stand outside burnt houses following an attack by the Islamic militant group Boko Haram in Gambaru, Nigeria on May 11, 2014. Jossy Ola/AP The Nigerian jihadist group Boko Haram killed at least 86 people in a series of attacks earlier this week.

The attack, in which the group firebombed villages and reportedly burned several children to death, is the latest demonstration of the brutality of a group that's killed over 15,000 people in the past 14 years, and has emerged as one of the deadliest terror organizations on earth.

Every terrorist group inhabits its own moral universe, following a value system and worldview that compels it to kill.

But Boko Haram's atrocities are heinous enough to upend the claim that terrorist violence stems from something that can be rationalized or comprehended.

The group kidnapped over 200 girls from a school in northeastern Nigeria in April of 2014, massacred as many as 2,000 villagers during a single attack along the shores of Lake Chad in January of 2015 and may have used a 10-year-old girl as a suicide bomber in July of 2015.

A screen shot of a video released by Boko Haram shows kidnapped Nigerian school girls. Twitter Boko Haram, which pledged allegiance to ISIS in March of 2015, seems to exist on the edges of human depravity, outside of any comprehensible moral system.

But that's not the case. In an important new Brookings Institution study, Georgetown University scholar Alex Thurston gives a compelling analysis of Boko Haram's ideology and worldview.

Through an analysis of the group's literature and the statements of top Boko Haram leaders, Thurston shows that the organization's ideology has remained remarkably consistent since its founding in 2002, with the group using a "combination of exclusivsm and grievance" to justify "violence toward the Nigerian state, other Muslims, and Christians."

Here's what that means.

Boko Haram attacks and safe haven as of mid-2015 Reuters

Boko Haram vs. everybody else

As Thurston notes, Boko Haram wasn't the first Salafist, or ultra-conservative reformist Islamic movement to gain traction in northern Nigeria.

It set itself apart through its opposition not just to western norms and secular government, but also through its ideological hostility towards nearly every other Islamic group in the region, regardless of its political or social orientation.

Simply, Boko Haram "consider themselves the only genuine representatives of Sunni Islam," Thurston writes, and "consider themselves arbiters of who is a true Muslim."

For Mohammed Yusuf, the Boko Haram founder who died in Nigerian government custody amid a 2009 crackdown against the group, "loyalty to Islam meant rejecting democracy and Western-style education."

He believed that "'ruling by other than what God revealed' is equivalent to polytheism," and that "democracy positions the people as an authority in rivalry with God."

Nigerian soldiers man a checkpoint in Gwoza, Nigeria, in April 2015, when the town was newly liberated from Boko Haram. AP Photo/Lekan Oyekanmi One crucial difference between Yusuf's ideas and other strands of Salifism was his belief that Muslims are obligated to act against western or secular authority, and that they "needed to confront the fallen society surrounding them." Quietism is just not an option within the Boko Haram worldview, which views even passive acceptance of the status quo as an unforgivable crime.

As Thurston notes, Boko Haram's novel interpretation of Islam — which is more extreme and far more activist than other strands of Nigerian Salafism — was enabled through a "'fragmentation of sacred authority' in Northern Nigeria." The region's Sufi orders, or mystical sects, as well as its system of traditional authority shared among a group of centuries-old emirates in the country's Muslim north, had seen their influence wane in the decades leading up to Boko Haram's rise.

Boko Haram didn't just attempt to surpass the Sufi orders and emirs. It actively rejected and turned on them, even assassinating the Emir of Gowa in May of 2014.

Boko Haram, savior of Nigeria's Muslims

Of course, plenty of other other religious movements around the world have viewed themselves as the only true embodiment of spiritual and doctrinal purity — and Boko Haram has been more brutal than almost all of them. The group's victim complex, which is central to both its ideology and its self-image, helps explain why.

As Thurston writes, "Boko Haram's leaders tell a provocative story about what it means to be Muslim in Nigeria."

Yusuf had argued that "The government of Nigeria ... has been built to attack Islam and kill Muslims," After Yusuf's death, his successor, Abubakr Shekau, cast Boko Haram's struggle as a fight for basic religious liberty in the face of an aggressive central government, saying in a 2012 speech that the government is "fighting us for no reason, because we’ve said we’ll practice our religion, we will support our religion and stand on what God has said," according to Thurston.

Nigeria, which is the most populous country in the world with an even demographic split between Muslims and Christians, has a fraught regional and sectarian politics that lends just enough credence to these claims to make them seem plausible to possible recruits.

Certainly Yusuf's 2009 death increased Boko Haram's sense that it was being specifically persecuted by the authorities — which, according to Boko Haram's moral framework, meant that virtually the only true Muslims in northern Nigeria were being singled out and attacked as well. As Thurston's analysis shows, the group still maintains that it's fighting for the survival of Islam in Nigeria against a host of forces attempting to exterminate it.

Abubakar Shekau, the leader of Boko Haram, pledges allegiance to ISIS caliph Al-Baghdadi. screenshot Thurston's analysis leads to a number of distressing conclusions. Boko Haram's rise, and its brutality, doesn't stem from the political or economic situation in northern Nigeria, or even from the influence of outside groups like Al Qaeda or ISIS.

Instead, it was driven by an ideology that cropped up organically in Nigeria — an ideology that reflects a coherent theory of religion, reality, and politics.

It's a worldview that tries to answer fundamental questions about the individual's role in society, the nature of an ideal state, and the relationship between religious imperatives and earthly action.

Like ISIS, another jihadist group whose worldview exhibits a certain jarring coherency, Boko Haram is sustained through a set of ideas — something that might allow Africa's most brutal jihadist group to survive even after it loses its remaining safe havens around Lake Chad.