UNGWAN GATA/ABUJA Nigeria (Reuters) - When Fulani raiders carrying rifles, machetes and clubs stormed his village one night last month, Pius Nna was stunned to see his teenage nephew among them.
"He was leading them and telling them to check very well, because my house would have a lot of people in it and they would be sure to find someone to kill," said Nna, a tall farmer in his mid-60s who said he escaped by fleeing into the bush.
Sitting in a courtyard littered with rubble, Nna told how his sister's son, whose father is a Muslim Fulani, had led the raiders to burn down his farm in the attack on Ungwan Gata village, one of several mostly Christian Moro'a communities in Nigeria's central Middle Belt.
The March 14 raids by Fulani herders on Ungwan Gata and two other villages killed at least 149 people, locals and officials said. Fulani leaders said their own people had been attacked previously and had a right to defend themselves.
Feuding over land and resources between rival communities in the Middle Belt has killed tens of thousands since independence from Britain in 1960. Fueled by ethnic and religious antagonisms, the violence has been compounded since 2009 in Africa's No. 1 oil producer by a spreading Islamist insurrection in the northeast, led by a group called Boko Haram. That insurgency has killed thousands.
The escalation of conflict, sometimes splitting tribes and families, is straining the divide between Nigeria's largely Muslim north and Christian south and its future as a unified state, recently declared Africa's largest economy.
On April 14, a bus station bombing on the edge of the federal capital Abuja killed at least 75 people. Boko Haram claimed responsibility for the attack, which was followed the same day by a mass abduction of teenage schoolgirls in northeast Borno state, suggesting the state is losing ground against the violence.
A statement following a meeting on Thursday between President Goodluck Jonathan, his security chiefs and all of the country's governors called the surging violence a "war on all Nigerians", urging them to keep religion out of all conflicts.
A Christian southerner whose 2011 election triggered deadly riots, Jonathan may run again in a February 2015 vote which many fear will exacerbate political, ethnic and religious enmities racking Africa's most populous country.
"EXPLOSIVE FORCES"
Nigeria, named and created by its British colonial rulers in 1914, was always an artificial formation patching together disparate and often historically antagonistic peoples - principally the largely Muslim Fulani, Hausa and Kanuri of the North, and the Yoruba, Igbo and other peoples of the now mostly Christian south, roughly split across the Middle Belt faultline.
"Nigeria was formed by Britain out of irreconcilable peoples ... these people came to find that, following British rule, the differences among them, far from shrinking, became accentuated, and ... the structure left behind by the British finally was unable to contain the explosive forces contained within it," wrote journalist and author Frederick Forsyth in "The Biafra Story", his 1969 history of the Biafra war.
The 1967-1970 Biafran war, in which the Ibgo easterners tried and failed to form their own breakaway independent state, was the first great rent torn in Nigeria's independence unity.
So far, Boko Haram's northern revolt has not threatened the basis of Nigeria's economic riches, the oil-rich creeks and offshore fields in the south. Niger Delta rebels seeking a greater share of this wealth signed a 2009 peace deal after a campaign of sabotage and violence.
But with violence intensifying and an election coming up in February, there are fears that what Forsyth called Nigeria's "attempted marriage of the irreconcilables" will be tested.
"NIGERIA WILL NOT DIVIDE"
Jonathan says Boko Haram will not "disintegrate" the nation. "Nigeria will not divide," he said in an Easter speech.
In a sign the currents of violence may feed from each other, Boko Haram has invoked lack of justice in Middle Belt killings as justification for its attacks on Christians, including bombings against churches in Plateau and Kaduna states.
Leaders of Christian "indigene" groups say they fear the spread southwards of Muslim Hausa-Fulani is an attempt to impose on them the Islam and sharia law that dominates northern states.