WASHINGTON — Nigeria is arguably the worst run of the world’s seven most populated countries. Despite earning hundreds of billions of dollars in oil revenue over the past decade, it is expected by 2015, by some calculations, to have the second-most destitute people in the world after India. But its largest city, Lagos, which until recently was known as one of the world’s most difficult cities to govern, seems to have turned a corner.

Even though it remains a slum-ridden and largely impoverished metropolis, with an exploding population estimated at 21 million (of Nigeria’s 170 million people), it has seen steady improvement in its governance for over a decade. The government has enhanced public transportation, cleaned up streets, upgraded the business environment and bettered the lives of its inhabitants.

So Nigeria, of all places, may be pointing the way to a strategy by which fragile states might begin to succeed: Devolve more power to cities from their corrupt and overcentralized national governments. At least in democracies, the cities have promise because their elected politicians face pressure to deliver specific services to their constituents. In the central governments, which are more remote, there is too much power and wealth to be grabbed by dysfunctional politicians and their cronies, and too little direct accountability.

The emergence of fragile states is one of the world’s most pressing problems. Such states, which include Nigeria, Iraq and Yemen, contain a rising number of the world’s poor (half of the world’s people who live on less than $1.25 a day will be in fragile states by 2015, according to the Organization for Economic Cooperation and Development) and contribute disproportionately to the world’s instability and terrorism. They have become a major focus of international aid efforts, but it has proved very difficult to improve governance there.