ABUJA A decisive election victory by President Goodluck Jonathan in Nigeria has shifted power firmly to the largely Christian south from the Muslim north and could reopen political fissures in Africa's top energy supplier.
Violence swept northern cities, leaving hundreds of people dead and many homeless after Jonathan's crushing victory over his northern opponent Muhammadu Buhari, a former military ruler.
"Jonathan's landslide, though on the surface it appears like a resounding pan-Nigeria mandate, has brought back with a vengeance all the religious and sectional cleavage, not to mention ethnic bitterness," Olakunle Abimbola of The Nation newspaper wrote in a column.
Many people see the riots as a reaction by the north to being cut adrift from power and say Jonathan will have to tread gingerly to avoid fuelling resentment in the vast impoverished area.
So far the president has said his victory is for all Nigerians and his aides have refrained from being triumphalist.
Although Buhari won in almost all Nigeria's northern states, Jonathan also picked up millions of votes and his northern backers -- particularly in the elite -- have high expectations.
"His inauguration as president on May 29 will be payback time," a senior member of the Arewa Consultative Council, a northerner leaders forum, told Reuters.
"To win the presidency on the first ballot, as he did, he met many times with northern leaders and made many promises. One of the concessions is that he will serve one term which we will hold him to," said the member, who asked not to be named.
The council, some of whose top members were targeted in the post election violence for backing Jonathan against Buhari, was counting on the north getting key posts and projects, the member added.
"It will be quite difficult for him to govern because there are so many interest groups to satisfy," the member said.
After independence from Britain in 1960, the understanding among Nigerians for many years was that the less advanced north held political power, while the south, where Christianity and Western-style ideas have long held sway, controlled the economy.
But that implicit north-south deal was always on shaky ground.
Southern soldiers staged Nigeria's first coup in January 1966, killing mainly northern political and military leaders.
That sparked a 30-month civil war, killing more than a million from fighting and starvation, ending with the north firmly in control when the breakaway Biafra republic surrendered.
The north-south balancing act faced another challenge when self-made billionaire Moshood Abiola, a Yoruba from the southwest, won a presidential vote on June 12, 1993.
Alarmed, the generals in power at the time annulled the vote and within a few months the diminutive dictator General Sani Abacha seized power and clamped Abiola in jail, waving aside local and international appeals to free the election winner.
Both men died mysteriously in 1998 within a month of each other, in Abiola's case in prison, triggering riots in his Yoruba stronghold in and around Lagos, Nigeria's biggest city and commercial capital.
Their demise, however, cleared the deck for the restoration of democracy in 1999, with a tacit understanding by the dominant PDP party that power would switch between north and south, each serving two four-year terms.
Olusegun Obasanjo, a southerner, duly served two terms as president and was succeeded by an ailing northerner, Umaru Yar'Adua, on whose death, Jonathan, then vice president, took over last year as stipulated by the constitution.
Some northern politicians demanded he serve out Yar'Adua's term and stand down to let the north back in. Instead the former university lecturer stood and won the PDP nomination and then the presidency.
"In the south, we are feeling liberated from many years of northern rule," retired businessman Joshua Ajayi told Reuters.
Now the north appears to have lost political power and has no economic levers to compensate for it.
The vast region is in tatters, with most of its agriculture shriveling due to neglect and dry conditions especially in areas close to the Sahel region.
Children, encouraged by an Islamic culture of alms giving, roam northern cities begging for handouts, an uncommon sight in the south where people tend to fend for themselves.
Years of hydrocarbon exploration in the Lake Chad region in the north, where oil is being exploited on the other side of the border, has not yielded anything that can be commercially mined.
In contrast, large, bustling industrial cities like Lagos, Port Harcourt and Onitsha continue to thrive in the south and attract migrant workers and business activity.
"The president had better summon the political will to set into motion radical processes to restructure Nigeria along productive federal lines, instead of being lulled by a false dawn of a 'pan Nigeria' mandate," The Nation's Abimbola said.
And managing the north-south split is far from his only challenge.
Jonathan is the architect of an amnesty for insurgents that has halted militant attacks on oil installations in the Niger delta, his home turf, where nearly all of Nigeria's economic lifeblood oil and gas is produced.
Many people will be looking to him to use his mandate to end once and for all hostilities that nearly paralyzed Africa's biggest oil and gas industry.
Also crying out for his attention is a lack of public power supply, which Jonathan has long promised to remedy, as well as corruption, which many say are Nigeria's two main drawbacks.
"He has to fight corruption," said Rilwan Musa, a political analyst from the north.
(Editing by Nick Tattersall and Andrew Heavens)