It’s a blazing hot Monday afternoon, the temperature topping 110 degrees in the deserts of southern Arizona, and Maria Rodriguez is on a mission of mercy. She’s delivering a huge load of dog food to the Mexican border town of Sasabe, Sonora. By her count, some two hundred and fifty stray dogs roam the streets hunting for whatever food they can find to stay alive. The town itself has largely been abandoned. Shootouts between cartel factions fighting to control smuggling routes into the U.S. have reduced the population of almost a thousand people to about fifty, in Maria’s rough estimate....