Reporting from Monterrey, Mexico -- The small houses of the Independencia neighborhood climb a hill that rises from the bone-dry Santa Catarina riverbed. Gang graffiti proliferate the higher you go, until they completely cover the cinder-block walls with slogans, threats and declarations. Young men in baggy pants, sweat shirt hoodies pulled tightly around their faces, populate the desolate street corners, in between vacant lots and shattered wooden stoops. Look out from the top of the hill and in the distance you see the impressive skyline of Monterrey, the wealthiest city in Mexico, its fancy museums, glistening high-rises, leafy plazas and...