Nigeria Finds a National Crisis in Every Direction It Turns

Mr. Buhari’s government has said it is open to negotiating with the group. But it is already stretched thin.

On the opposite side of the country, Boko Haram is still raging. Mr. Buhari has started a major offensive against the group that has made progress, but it has yet to stamp out the violence.

Another longtime battle is flaring in the middle of the country, between farmers and nomadic Fulani herdsmen looking for grazing pastures. Hundreds have been killed in battles as herdsmen roam into new territory to look for vegetation for their cattle. Officials have blamed climate change and the nation’s rapidly growing population for the scarcity of pastureland.

And with their demands for economic equality for the south, the Avengers have been trying to stoke the aspirations of separatists elsewhere in the nation.

More than four decades ago, at least one million people were killed during the Nigerian civil war, when separatists led an uprising that created an independent republic of Biafra in the southeast. It lasted three years, until 1970.

Now, a Biafran separatist movement is simmering again, with the police and protesters clashing regularly since October, when a prominent activist was arrested and jailed. Some have accused the Nigerian security forces of seeking out and killing protesters.

The Avengers are fanning the separatist sentiments, invoking the Biafran movement and calling for a “Brexit”-style referendum to split the nation along several fault lines.

Ugborodo, Nigeria, houses a Chevron terminal, but the town’s residents say they have seen little benefit.

The south has long been a reservoir of anger and resistance, a place where countless billions in oil revenue are extracted for the benefit of distant politicians and companies abroad. Yet drinking water and electricity can be scarce, and the swamps people live around are regularly polluted with Exxon Valdez-size spills, casting an oily sheen on the creeks and coating the roots of dense mangroves in black goo.

Many people in the predominantly Christian south say they believe that Mr. Buhari, a Muslim from the north, is neglecting them for political or sectarian reasons, even though conditions were also grim under his predecessor, Goodluck Jonathan, a Christian southerner.

“You always say you fought for the unity of this country during the civil war,” the Avengers taunted Mr. Buhari on their website. “You haven’t been to the Niger Delta, how can you know what the people are facing.”

In his recent speech, Mr. Buhari recalled the horrors of the civil war, when he served in the military fighting Biafrans. “The president has a vision of one united Nigeria and is prepared to do everything to keep it as one,” he said.

This spring, Mr. Buhari announced that he would personally introduce a $1 billion cleanup program of the oil-polluted Niger Delta area. It was to be Mr. Buhari’s first visit to the region since taking office, but with the Avengers’ movement raging, the president abruptly canceled his trip. Residents of Delta State felt slighted.

“Years have passed with neglect, deprivation, environmental deprivation, poverty, no electricity, no roads, no hospital, no schools, but we are living in the country of Nigeria,” said Blessing Gbalibi, a fuel-truck driver raised in the creek communities. “Over there in Abuja,” he added, referring to the capital, “they are taking our resources.”

Yet many Niger Delta residents like Mr. Gbalibi oppose the Avengers because their acts of sabotage have degraded the already-poor quality of life in the region. Spills from explosions have further polluted farmland and fishing holes. Mr. Gbalibi and his fuel truck were among those stuck on the side of the highway for a month because the Avengers had disrupted fuel distribution.

A store in Ugborodo. Residents of the Niger River Delta feel neglected by the government in Abuja.

About a decade ago, another band of militants, the Movement for the Emancipation of the Niger Delta, prowled the creeks, blowing up pipelines. The federal government reined it in by setting up an amnesty program that offers cash and job training, some of it overseas, for more than 30,000 militants and residents, according to Paul Boroh, a retired brigadier general and the special adviser to Mr. Buhari for the program.

But oil revenue finances the program, and the fall in oil prices prompted the president to consider ending the amnesty program at the end of last year. Mr. Boroh said he had lobbied to keep the plan for now, but to phase it out over the next two years.

The Avengers movement sprang up around the time the president was considering an end to the program, prompting many Niger Delta residents to wonder if the shadowy group is made of former militants hoping to keep up amnesty payments.

The amnesty program is far from universally loved in the creeks. Many residents say payments are routinely siphoned by corrupt community leaders. Others say the job training they received was virtually useless. Oil companies prefer to hire foreigners, they complain, or they hire locals only on a short-term basis — and then nothing.

The program sent Mike Gomero, a former militant, to learn the teachings of Mohandas K. Gandhi and the Rev. Martin Luther King Jr. at a two-week session in South Africa. He is no longer blowing up pipelines. But he still does not have a job.

“The amnesty program is not a solution,” said Williams Welemu, a former member of the Movement for the Emancipation of the Niger Delta. “It’s palliative.”

Communities like Ugborodo, so deep in the winding creeks that it is at least two hours from the mainland by speedboat, are dotted with homes that are little more than tiny zinc huts on islands that are sinking into the sea. They are filled with unemployed residents trained as geologists, pipe fitters and marine engineers.

One of them, Collins Bemigho, stood along a dirty swamp, orange flares from a giant Chevron terminal glowing in the distance behind him. He complained about a lack of indoor plumbing, of good health care or a secondary school, and then pointed to a thick pipe jutting from the water.

“If I wanted to bust a pipeline, I could do that right here,” Mr. Bemigho said. “We’re not rewarded for being well behaved.”