Now it struggles to keep security within its own borders as an Islamist insurgency in the northeast kills thousands.
A lack of investment in training, failure to maintain equipment and dwindling cooperation with Western forces has damaged Nigeria's armed services, while in Boko Haram they face an increasingly well-armed, determined foe.
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A foe that abducted more than 200 secondary school girls in Chibok, northeastern Nigeria, nearly a month ago. The military still appears to have no idea exactly where they are, but denies it lacks the capacity to get them back.
President Goodluck Jonathan has said that Boko Haram has "infiltrated ... the armed forces and police", sometimes giving the militants a headstart, but the problems go much deeper.
"The Nigerian military is a shadow of what it's reputed to have once been," said James Hall, a retired colonel and former British military attache to Nigeria. "They've fallen apart."
Unlike Nigerian peacekeepers in the 1990s, who were effective in curbing ethnic bloodshed in Sierra Leone and Liberia, those in Mali last year lacked the equipment and training needed to be of much use in the fight against al Qaeda-linked forces, sources involved in that mission say.
Hall said the Nigerian peacekeepers had to buy pick-up trucks and their armour kept breaking down. They spent a lot of time on base or manning checkpoints.
Military education is still taken very seriously, he said, but equipment and training to use it have been neglected, with radio equipment in particularly short supply.
Army spokesman Brigadier-General Olajide Laleye recognised some of these problems in a news conference on Tuesday. He said the army would "undertake an equipment audit ... with a view to identifying areas where equipment and material are in short supply, unserviceable or even obsolete".
The defence headquarters did not respond to a request for comment, but the military argues that counter-insurgency is something new that they are slowly learning to take on, just as the U.S. military had to learn they couldn't fight al Qaeda in western Iraq using conventional warfare.
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"They're having to learn new counter-insurgency skills and get new equipment ... like armoured vehicles," said Kayode Akindele of 46 Parallels, a Lagos-based investment management firm that also consults on financial, political and security risks for foreign investors.
The militants know the military's limitations. A police source said a fighter jet flew over the market town of Gamburu on Monday as a group of gunmen killed at least 125, but the killers didn't flinch, knowing they could not be targeted while scattered in a densely populated area.
President Jonathan declared a state of emergency in the northeast a year ago, ordering extra troops, but security sources say the armed forces remain overstretched. Perhaps as few as 25,000 service-ready troops face an insurgency over a wide area in the northeast, communal violence across north and central Nigeria and rampant oil theft in the south, as well as commitments to peacekeeping missions, one security source says.
Morale is also a problem, says a ground soldier deployed in the northeast who did not wish to be named.
He said the food was bad, sleeping conditions rough, very few people get the leave to which they are entitled, and they live in constant fear of Boko Haram attacks.
"There is just a kind of hopelessness hanging over us," he said.
Not so their adversaries, whose fearless determination is fuelled by dreams of jihadist martyrdom.
"In a typical unit, Boko Haram has between 300 and 500 fighters. It's not a guerrilla force that you can fight half-heartedly," said Jacob Zenn, a Boko Haram expert at U.S. counter-terrorism institution CTC Sentinel. "It's snowballing. It's getting more weapons, more recruits, their power is increasing every day."
On Feb. 12 dozens of fighters loyal to Boko Haram attacked a remote military outpost in the Gwoza hills. A security source with knowledge of the assault said they came in Hilux tracks with mounted machine guns and showered the camp with gunfire.
Boko Haram's fighters had little cover and were easily picked off - 50 of them died against nine Nigerian troops – but they still managed to make off with the base's entire armoury stockpile of 200 mortar bombs, 50 rocket-propelled grenades and hundreds of rounds of ammunition, the source said.
Their ability to dart over the border into Cameroon, whose own security forces have shown little appetite for taking them on, gives the militants an added advantage.
Ethnic and religious divisions within the military have also bred some collusion with Boko Haram, sources say. An artillery soldier said units were sometimes suspiciously ambushed. He is convinced "someone in command leaks our plans to terrorists".
"The military, just like the rest of Nigeria, is fractured, which means it probably does have Boko Haram sympathisers within it," former U.S. Ambassador John Campbell said.
The military isn't that short of money on paper. In 2014 security will swallow nearly 938 billion naira ($5.8 billion), a quarter of the federal budget. Of that, the defence ministry will take more than a third, but only 10 percent is for capital spending.
A government advisor says there was some evidence a few senior officers were pocketing money meant for equipment, so corruption may also be a factor in the shortfalls.
A senior security official, who declined to be identified, said the process of decline in the military has been gradual, starting when the military seized power in the 1960s.
He said Britain, France and the United States had been Nigeria's main military assistance partners, but they gradually backed off from its increasingly quirky and corrupt military dictators, culminating with the venal Sani Abacha in the 1990s.
In the 21st century, Nigeria, now democratic, can be prickly about meeting conditions on military assistance packages, Western diplomats and military officials say, such as giving Western trainers full access to its bases, intelligence sharing and improving its human rights record.
"The human rights issue has been a point of friction for a long time," said one U.S. military official, speaking on condition of anonymity.
The military has repeatedly denied allegations of abuses such as summary executions, but Amnesty International condemned the alleged killing of hundreds of prisoners escaping from Giwa barracks last month. The military said it had no choice but to prevent their escape.
Foreign aid aside, decades of coups made unstable military regimes fear their own armed forces. Each coup plot led to a deliberate under-resourcing of any department under suspicion.
A botched 1985 counter-coup against newly installed Ibrahim Babangida was rumoured to involve planned aerial bombardments, so his junta cut funds to the air force, a security official who remembers the time says. Another failed coup in 1990 allegedly involved military police, so their budget was squeezed.
When democracy returned in 1999, President Olusegun Obasanjo, himself a former military ruler, feared the army, too. "This starvation of the military has occurred since Obasanjo, as part of a strategy to ensure they couldn't conduct more coups," Campbell said.
Now, as families in Chibok pray for the return of their kidnapped daughters, some fear it may be beyond their armed forces to get them back, and welcome promises of assistance from China, Britain, the United States and France.
"We don't believe there is a serious effort at a rescue, “said Lawan Abana, whose two nieces are among the abductees. "The Americans and the others are our last hope."