When U.S. law enforcement officials last month busted a Mexican drug cartel moving tons of dope and millions of dollars, they announced it in Atlanta. The distribution ring stretched from Colombia to New York to Italy, but the operation’s key hub was Atlanta. Long a commerce and transportation center for giants like UPS and Delta Air Lines, Atlanta tags itself as an “international city.” This time, it embodied that definition in an illicit way. Federal drug agent Jack Killorin calls Atlanta “the new Southwest border.” ... Mexican distribution rings supply about 90 percent of the cocaine, 80 percent of the...