War against Zetas fueling surge in violence along Rio Grande
                                
                                
                                    (Newser) -
                                    Three of Mexico's warring drug cartels have agreed to stop shooting each other for as long as it takes to wipe out a fourth, up-and-coming cartel, the  BBC  reports. Anti-narcotics authorities say that the Sinaloa, La Familia, and Gulf cartels are seeking to exterminate the Zetas, a breakaway group of...