It’s now official — Muhammadu Buhari, the former military head of state from 1983 to 1985, has won the Nigerian presidency in the closest election since the return of civilian rule in 1999. Buhari will be the first northerner to hold the office since the 2010 death of Umaru Musa Yar’Adua.

It’s impossible to overstate just how important today’s election results are for Nigeria, for sub-Saharan Africa and for developing democracies. As an important partner for regional stability, Nigeria is one of the most vital allies of the United States in Africa today, even as it faces a handful of incredibly delicate security, economic and sociocultural challenges.

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With only the troubled northeastern state of Borno left to report results (a state that Buhari is expected to win easily), Buhari had 53.24% of the vote to just 45.67% for Jonathan, and he won not only the northern pro-Buhari states, but much of southwestern Nigeria as well (Buhari won the states marked in green below, Jonathan the states in red). Though the opposition, now merged as the All Progressives Congress (APC) already controlled Lagos, the governing People’s Democratic Party (PDP) of incumbent Goodluck Jonathan traditionally wins greater support in the southwest.

So what does this mean for Nigeria and for Africa?

A great day for African democracy. This is quite obviously a huge step for democracy in Africa. Nigeria is the most populous country on the continent, and it’s now the largest economy in Africa. It’s hard to talk about growing democratic norms in sub-Saharan Africa if its biggest country features one-party rule and rigged elections. Jonathan has already conceded defeat to Buhari. But a sustained peaceful transfer of power from Jonathan to Buhari (pictured above, right, with Jonathan, left) would be the first such transfer from a defeated president to a successful challenger in Nigerian history. It’s huge — and massively important that both Jonathan and Buhari succeed. Despite Buhari’s past role as a military dictator in Nigeria, he has routinely reaffirmed his commitment to civilian rule and to democracy — most recently at a talk in London at Chatham House late last month. Having waged three previous unsuccessful presidential campaigns since the return of civilian rule in 1999, there’s every reason to believe Buhari. But the world will be watching, and Buhari’s restrained and democratic exercise of executive power will reinforce the rule of law and democracy in Nigeria.

Voters lost confidence in Jonathan’s ability to defeat Boko Haram. This was an election above all about security. Nigerian voters have lost confidence in the Jonathan administration’s capability to effectively stop the Boko Haram insurgency in the northeast, and the only progress made during the election’s six-week delay came not from the Nigerian military but from the Chadian military and other outside forces. There’s no guarantee that Buhari has the requisite tools to subdue Boko Haram. But as a northerner and as a pious Muslim, Buhari will have much more goodwill among local leaders in the north than Jonathan ever did. As the federal government is so much more powerful than local government, Buhari’s election will signal to northern Nigeria that it should expect more investment from Abuja in the years ahead, and that too will take some of the steam out of the insurgency. After all, it’s a lot easier for Boko Haram to contrast itself against Jonathan, a southerner, than a Muslim who supported the move by many northern states in the early 2000s to introduce at least some mild forms of shari’a law. But northern Nigeria has been underdeveloped since the days of British colonialism compared to the southwest, and Buhari would be well advised to move aggressively to build infrastructure in the form of additional schools, hospitals and transport links.

Expect a much-needed anti-corruption push. Buhari is genuinely committed in the fight against corruption, and his attempts to stymie government graft in the 1980s are chief among the reasons that he, in turn, was deposed by a coup in 1985. If Buhari’s victory comes primarily from the sense that he can more effectively defeat Boko Haram, it comes secondarily from the sense that Buhari will try to roll back the massive corruption for which Nigeria has become known. Buhari’s record in office in the 1980s is far from perfect — he introduced draconian restrictions on press freedom, for example. But he also attempted to build Nigerian institutions and the civil service. Expect Buhari to turn his focus to similar initiatives in 2015 — having become the somewhat unlikely face of Nigeria’s deepening democratization, he now has the chance to introduce reforms to deepen the rule of law and tamp down the corruption that’s wasted the country’s oil wealth and that hinders foreign investment (outside of the oil industry, at least).

Obasanjo delivered. Without the support of many former members of Jonathan’s ruling PDP, Buhari would not have won this election. That includes Olusegun Obasanjo, Nigeria’s president from 1999 to 2007, who once counted Jonathan among his protégés. Obasanjo quit the PDP earlier this year and announced his support for Buhari. A wily operator and a respected statesman in the region, Obasanjo has always sought to maximize his post-presidential power, and his decision to back Buhari can best be understood in that context. Buhari now owes him a great deal, especially in the fight to win votes in Nigeria’s pivotal southwest (outside of Lagos, at least). He also owes many other national and local leaders, including, amazingly, Ibrahim Badamasi Babangida, the northerner who ousted Buhari from power in 1985. Many of these leaders will expect a handsome reward from the new Buhari administration, which risks perpetuating the cycle of political graft in Nigeria. Insofar as Buhari will continue to need their support going forward (legislative elections will follow in mid-April, and there’s little uniting the APC other than opposition to Jonathan), it could complicate Buhari’s efforts to reduce corruption and improve government.

Don’t forget Nigeria’s southeast. As if Nigeria’s finances, corruption and Boko Haram weren’t enough, Buhari will also face an additional risk. Like the north, Nigeria’s oil-producing Niger Delta has historically been one of the poorer regions of the country. Jonathan, a member of the Ijaw ethnic group (a minority in Nigeria’s southeast), was the first president to come from the region, and he’s one of just two presidents to arise from Nigeria’s southeast. That hasn’t fully becalmed the region over the past six years while Jonathan has been president, but it has significantly reduced tensions in Rivers State, the heart of the oil-producing region and its capital city of Port Harcourt. In the winner-take-all sweepstakes of Nigerian elections, southeasterners will believe, perhaps with some truth, they have lost the most with Buhari’s victory. So one of Buhari’s first priorities will be to reassure southeastern Nigerians, and residents of the Niger Delta in particular, that he won’t allow the region to stagnate. If he doesn’t, Buhari will find soon that he has a southeastern insurgency just as harmful to national unity as the Boko Haram insurgency.