NIGERIA, Dec. 9 -- Nigeria shocked the world this week. For months, Abuja had been warning powerful nations, especially the United States, to respect our sovereignty and territorial integrity. Yet, overnight, the same Nigeria ordered its Air Force jets across the border into Benin Republic to defend democracy from collapsing.

This single event, swift, bold, unquestioned, has exposed a truth we can no longer run away from: a country that can project power beyond its borders has no excuse for failing to secure its own people at home. If Nigeria can prevent a coup in a sovereign neighbour, then what explanation remains for the unending banditry, insurgency, kidnapping and carnage tearing across the North? Why does the state become strong in...