For the first time since Nigeria won its independence in 1960, the country has inaugurated an opposition figure as its next president.
Muhammadu Buhari, a retired general who ruled the country back in the '80s after a military coup, was sworn in as president of Nigeria on Friday.
"He has taken over from Goodluck Jonathan, who urged his successor to unite the country in the face of the threat from Boko Haram militants. Mr Buhari, a former military ruler, says he is a convert to democracy.
"He defeated Mr Jonathan - who had been in office since 2010 - by 15.4 million votes to 12.9 million.
"The BBC's Will Ross in the capital, Abuja, says heads of state and senior government officials have come from across the world to witness this truly historic moment for Nigeria. In a country with a [checkered] history when it comes to power changing hands, this is a chance to celebrate deepening democracy, he says."
Reuters reports that during his inaugural address, Buhari said that Nigeria "needs careful management to overcome the impact of low oil prices, slowing growth, high unemployment and the security threat from Islamist group Boko Haram."
CNN reports that Buhari's military experience may have played a role in his election. The network explains:
"Before the election, African affairs analyst Ayo Johnson said Buhari's military background may be what voters need to feel safe from the deadly Boko Haram militant group.
"'Many Nigerians will not forget he was a military leader, during a dictatorship,' Johnson said. 'Or maybe they will feel that they need a military leader to address fundamental problems such as terrorism.'
"This year alone, the extremists have killed at least 1,000 civilians mostly in the nation's northeast, where they operated freely, Human Rights Watch says."
Secretary of State John Kerry represented the United States at Buhari's inauguration. He tweeted: "Congratulations to @MBuhari & the Nigerian people. A privilege to be here to celebrate #Nigeria's historic & peaceful democratic transition."