In the late 1990s, Osiel Cárdenas Guillén, the former leader of the Gulf cartel, had other similar groups besides Los Zetas established in several cities in Tamaulipas. Each of these groups were identified by their radio codes: "the Rojos" (The Red ones) were based in Reynosa; "the Metros" were headquartered in [Matamoros; and "the Lobos" (The wolves) were established in Laredo. The infighting between the Metros and the Rojos of the Gulf cartel began in 2010, when Juan Mejía González, nicknamed "El R-1", was overlooked as the candidate of the regional boss of Reynosa and was sent to the "Frontera Chica," an area that encompasses Miguel Alemán, Camargo and Ciudad Mier – directly across the U.S.–Mexico border from Starr County, Texas. The area that Mejía González wanted was given to Samuel Flores Borrego, suggesting that the Metros were above the Rojos.