The Zetas traditionally operated in the state of Tamaulipas, along Mexico's north-east border with Texas, while under the auspices of the Gulf organization. Since the breakdown in its relationship with the Gulf organization, the organization has continued to battle the Gulf for control of Nuevo Laredo, and has also been pushed south into states such as Veracruz, Tabasco, and Nuevo Leon. The Zetas were previously the Gulf organizations armed enforcer wing. They are believed to have been created by several Mexican officers who deserted from the military's Special Forces division known as the GAFES. The group quickly expanded to include law enforcement personnel and civilians. The Zetas helped facilitate the Gulf organization's takeover of Michoacán, while in the process helping train La Familia, who would eventually turn on the Gulf organization.
As the Zetas grew more powerful, their relationship with the Gulf organization became more flexible allowing them to operate with a considerable degree of autonomy. They have expanded their activities to include training members of other criminal organizations in their specialized and often brutal tactics. In 2004 and 2005, the Laredo and Nuevo Laredo border region was plagued by a wave of violence due, in some part, to Zeta- led operations in the area. The Zetas have also challenged the Mexican military on several occasions using brazen tactics to assert their dominance in the region. Narco-bloqueos, or street blockades, have become common practice for Los Zetas in cities such as Monterrey and Reynosa.
The Zetas now face a challenge from a new and loosely formed alliance of convenience composed of on-again off-again rivals - the Gulf organization and La Familia - and their longtime competitors the Sinaloa OCG. The Zetas are believe to have the upper hand in some areas wresting control from the Gulf organization around Tamaulipas, and, according to some, are now believed to control around 70 or 80 percent of the state. Additionally, they have expanded their criminal enterprises to include human smuggling and extortion as U.S. and Mexican law enforcement has cracked down on narcotics smuggling and they have needed new revenue streams. Los Zetas' history of brutal violence will undoubtedly continue to manifest itself as the battle rages for control of narcotics trafficking routes along the eastern third of the U.S.-Mexico border.