The fight against Boko Haram is escalating, with troops from Niger and Chad crossing into northeastern Nigeria to fight the insurgency in a further sign that what began as a Nigerian problem has grown into a volatile regional one.

The troops began their push Sunday, a day after a series of suicide bombings in northeastern Nigeria killed as many as 100 civilians, and weeks before the country’s presidential election, which many worry could turn violent.

Boko Haram emerged in 2009 as a local insurgency, but it has increasingly become a regional threat, articulating wider ambitions. On Saturday, it declared its allegiance to the Islamic State fighters who have seized swaths of Iraq and Syria. Experts, however, described that pledge as little more than a rhetorical flourish.

The Ni­ger­ian fighters’ expansion across borders in recent months has been a wake-up call for Washington and for countries in the region, which had watched for years as a domestic military campaign failed to stamp out the group. Even as Boko Haram’s fiefdom within Africa’s wealthiest country grew to the size of Belgium, the Ni­ger­ian troops sent to fight it were poorly armed and sporadically paid.

Now, the militants’ bold attacks outside Nigeria have prompted a growing regional counterinsurgency effort that could finally weaken the Islamist radicals.

In recent months, the Ni­ger­ian fighters raided a Cameroonian military base and kidnapped the wife of the vice prime minister. They recruited herdsmen and farmers in Niger. They obstructed key trade routes in Chad, whose president, Idriss Déby, deemed the group “a permanent threat.”

Those countries initially began fighting Boko Haram on their own soil. But the operation by Niger and Chad signaled a new stage in the war — as well as implicit Nigerian acknowledgment that it was time to permit a foreign offensive.

Residents in Niger told the Associated Press they had watched at least 200 trucks full of troops from the two countries cross the border into Nigeria and had then heard large explosions.

“They are bandits and criminals who have nothing to do with religion,” Chadian Brig. Gen. ­Zakaria Ngobongue told reporters Monday in N’Djamena, the capital, after confirming his country’s role in the military campaign. Chad has conducted operations in Nigeria before, but not in conjunction with Niger.

U.S. training and arms

Some of the troops now embroiled in the fight against Boko Haram have received training and arms from the United States, which sees the group as a terrorism threat. But unlike Somalia’s al-Shabab, Boko Haram has little history of attacking Western targets, even though its name roughly translates to “Western education is sinful.” In spite of its incendiary rhetoric, the group’s goals are often hard to discern.

Even the size of the organization remains a mystery, with estimates ranging from 5,000 to 25,000 militants, although experts say the low-end estimate is probably more accurate. Nigerian officials say the fighters have retreated into a series of caves, emerging to conduct their attacks.

“It’s difficult to identify an endgame with Boko Haram. One characteristic they’ve shown over time is an ability to adapt to circumstance,” said Peter Lewis, the head of the African studies department at the Johns Hopkins School of Advanced International Studies. “Boko Haram is not one unified coordinated organization. They are a series of factions with different leaders and different armed groups.”

Chadian troops participate an annual training operation in N'djamena, Chad, on March 9. (Jerome Delay/AP)

Boko Haram killed roughly 10,000 people in 2014, most of them Ni­ger­ian civilians. The fighting forced more than 1 million to flee the country. That bloody ­period — exponentially more violent than previous years — drew pledges from the government that it would step up its fight against the group.

Air raids

Nigerian President Goodluck Jonathan has managed to dislodge Boko Haram from key training camps in recent months and has waged air raids on its remote strongholds. But it has been hard to assess the effectiveness of the counterterrorism effort because it is difficult to gain access to the affected areas.

A broader military coalition seems to offer more promise, but even Jonathan seemed to cast doubt last month on the prospect of regional collaboration, or at least joint operations.

“I don’t expect that all of us will come together, no,” he told the Wall Street Journal in an interview. “Chadians will be fighting from that end. The Cameroonians will also be fighting from that end.”

Still, many say Boko Haram has already suffered a significant blow from the neighboring countries’ militaries. Some see the audio message pledging loyalty to the Islamic State — released over the weekend by Boko Haram’s leader, Abubakar Shekau — as a sign of the group’s desperation.

“Shekau’s pledge is at least in part a cry for help, as Boko Haram is losing control of many of the residential areas it had captured since it began holding on to territory in July 2014,” said Martin Roberts, an analyst at IHS Country Risk.

For their part, U.S. intelligence officials viewed Boko Haram’s declaration of solidarity with the Islamic State with skepticism, noting that there is no evidence of meaningful ties between the groups and that Boko Haram has frequently sought to take propaganda advantage of high-profile affiliations with little follow-through.

“Boko Haram uses pledges of solidarity to get attention and weapons but has given up little control over its group or operations,” a U.S. intelligence official said, speaking on the condition of anonymity to discuss a sensitive issue. He added that the evidence of any contact between the group and the Islamic State is “pretty much nil.”

Boko Haram had previously made similar pledges of loyalty to al-Qaeda core organizations and collaborated with the terrorist network’s affiliate in North Africa, al-Qaeda in the Islamic Maghreb, known as AQIM. But when French forces began an assault on AQIM in Mali, many in Boko Haram quickly returned to the group’s base in Nigeria, U.S. officials said.

The Islamic State has reacted coolly to other efforts by Boko Haram to align itself with the Syria-based group’s brand. Cultural animosities would pose potential obstacles to a union between groups that are not known to have even exchanged emissaries, U.S. officials said.

Shekau has “resisted any efforts to be subsumed under any other terrorist group’s leadership or command and control,” the U.S. intelligence official said. “Even if he said, ‘We’ll take your orders,’ he wouldn’t.”

Greg Miller in Washington contributed to this report.

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