George Osodi/Bloomberg via Getty Images Gas flares burn from pipes at an oil flow station operated by Nigerian Agip Oil Co. Ltd., a division of Eni SpA, in Idu, Nigeria, in September. Nigeria was Africa’s biggest oil producer before attacks shrunk production.

Nigeria, already battling Islamist militants Boko Haram in the north, faces a resurgent uprising in its oil-rich south.

A shadowy militant group calling themselves the Niger Delta Avengers first emerged in February, when they blew up an underwater pipeline run by international oil giant Shell.

The group vowed to “cripple Nigeria’s economy,” and they already have. In the last three months, the Niger Delta Avengers claimed responsibility for pipeline attacks across the southern Delta region, and production dropped to 20-year lows.

Nigeria was Africa’s biggest oil producer before the attacks shrunk production. The government depends on oil revenues for around 70 percent of its budget, which was already squeezed by plummeting oil prices. The unrest has also exacerbated gas shortages and power outages across the country.

George Osodi/Bloomberg via Getty Images The group announced their arrival by blowing up a Shell pipeline in the Delta. Above, an employee at an oil flow station operated by Shell Petroleum Development Co. in Port Harcourt, Nigeria, in September.

The new militant campaign has also shattered seven years of relative peace in the Delta region, which has long been troubled by poverty, environmental destruction and unrest. A five-year insurgency in the Delta that erupted in 2004 saw dozens of oil workers kidnapped and thousands of people killed.

Here’s what we know about the Niger Delta Avengers:

Who Are They?

The Niger Delta Avengers claim to be a new group made up of youth from the region. “We are young, educated, well traveled and most of us were educated in east Europe,” one statement from the group says.

The Avengers have criticized previous Delta insurgent groups for working with the government, while ex-militant leaders urged the new group to halt attacks, saying they are a distraction from solving the region’s problems.

Even so, many locals believe the group is in fact made up of disgruntled former militants or local criminals seeking attention, according to the BBC.

Experts note that the level of coordination and technical expertise of the Avengers’ attacks suggests the group has help from sympathetic insiders at the oil companies.

What Do They Want?

The Niger Delta Avengers have vowed to continue attacks until oil firms leave the region, blaming them for the environmental destruction and economic marginalization of the Delta. “We will make you suffer as you have been made the people of Niger Deltans suffered over the years from environmental degradation, and environment pollution,” they warn international oil companies in one statement.

The group has also called for the Delta region to gain independence from Nigeria, reprising the hard-line demands of earlier insurgencies that had become much less common in recent years. "Their demands are impossible to meet so there will be probably more attacks," an anonymous security expert told Reuters.

A further complication is the emergence of various splinter groups, which have echoed the demands of older militant movements in the region. For example, one group calling itself the Egbesu Mightier Fraternity has demanded the release of a separatist leader from the nearby region of Biafra. Meanwhile, another group, Red Egbesu, called on anti-corruption authorities to stop pursuing a local warlord nicknamed Tompolo.

REUTERS/Tife Owolabi A man shows a bucket of crude oil spilled after a Shell pipeline leaked in the Oloma community of Nigeria's Delta region in 2014. Hundreds of oil spills each year caused catastrophic damage to the wetlands region.

Why Is This Happening Now?

Analysts suggest several possible reasons as to why the group has emerged at this moment in time.

First, militants in the region have been threatening to restart the insurgency since Nigerian President Muhammadu Buhari was elected last year, according to the International Crisis Group.

Buhari, who hails from northern Nigeria, replaced Goodluck Jonathan, Nigeria’s first president from the Delta region, and some Delta militants believe Jonathan’s electoral defeat was a conspiracy against the Delta, Crisis Group says.

Second, Buhari’s budget-tightening and anti-corruption measures have upset the Delta's ex-militants. The president has slashed funds to an amnesty program that since 2009 provided former fighters with a monthly stipend, and canceled lucrative pipeline protection contracts to companies run by ex-insurgents.

"The amnesty has failed,” a former pipeline attacker calling himself General Felix told Reuters last week, complaining that he hadn’t received an amnesty stipend in three months. "We are ready for a total showdown soon," he warned.

Afolabi Sotunde / Reuters A soldier stands guard in front of a banner with a picture of Nigeria's President Muhammadu Buhari in Gokana during the launch of a major oil cleanup initiative. It is expected to take 25 years.

How Has The Government Responded?

Buhari’s government has poured troops into the Delta to hunt down the militants, sending military helicopters and gunships into the region's wetlands.

But experts warn a military crackdown is unlikely to be effective, as the Avengers appear to be operating in small cells and hiding out in remote creeks.

Meanwhile, Nigeria’s security forces are already thinly stretched by fighting Boko Haram on the other side of the country, and are not familiar with the Delta’s swamps.

Diplomats and local activists also warn that a heavy-handed military crackdown could backfire by increasing local sympathy for the group. Local leaders accused the government this week of raiding their village and preventing the evacuation of the wounded. Meanwhile, the Niger Delta Avengers urged all militants not to engage in the kidnapping and violence that characterized previous insurgencies in the region, and denied the military’s claim that the group was behind a deadly attack on soldiers this week.

A more effective response would be to capitalize on rifts between the marginalized Delta youth and ex-militant leaders who got rich through the amnesty program, one security expert in Nigeria told Reuters.

The International Crisis Group has urged the government to address the root causes of the militancy, including the catastrophic environmental impact of hundreds of oil spills each year, and the crippling poverty and unemployment in a region that provides much of the country’s wealth.

The government this week launched a major cleanup operation in the region, but it is expected to take 25 years to repair the damage done by oil companies.

STRINGER via Getty Images The new Delta militant campaign has shattered seven years of relative peace in the Delta region, and the government has poured troops into the area.

How Have Delta Residents Responded?

Many Nigerians living in the Delta region say they have borne all the burden of Nigeria’s oil production, and received none of its benefits. Most Delta residents live on less than $2 a day.

But community groups have urged the government and militants not to let violence escalate. They called on Buhari, who canceled a visit to the region at the last minute this week, to make the Delta a priority.

"The events that are happening in the region pose serious economic, environmental and security challenges to the entire nation,” the Ijaw Youths Council, a group representing a major ethnic group in the Delta, said in a statement. "Aggrieved groups must give peace a chance.”

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