Nigeria, May 22 -- We like to lie to ourselves in this country. We clutch tight to sentimental stories of a united Nigeria and pretend that tribalism is a political invention, conjured up by greedy elites. "It's the politicians," we say, "they are the ones dividing us." And to prove our innocence, we share tales of solidarity: how strangers rush to save victims of a fire or accident, how people of different tribes mourn a lost child like their own. We showcase those fleeting moments of shared humanity as if they erase centuries of deep, complex mistrust.

But beneath the surface of those touching anecdotes lies a quiet epidemic we don't like to talk about. Ethnicity is not just alive-it thrives in whispers, in glances, in family meetings,...