When I first arrived in Mexico City last summer, it was still easy enough to believe that the madness of the drug war was a remote and relatively minor distraction: a dispute between rival cartels; a conflict largely confined to the border or distant mountain ranges that hide valleys of poppies and marijuana plants.

On a cold January evening, rain poured down onto the dimly-lit asphalt of Coney Island’s Mermaid Avenue, pooling in clogged gutters and dark, cigarette-stained alleys.