One of the first missions of Los Zetas was to eradicate Los Chachos, a group of drug traffickers under the orders of the Milenio Cartel, who disputed the drug corridors of Tamaulipas with the Gulf Cartel in 2003. This gang was controlled by Dionisio Román García Sánchez alias "El Chacho", who had decided to betray the Gulf Cartel and switch his alliance with the Tijuana Cartel; however, he was eventually killed by Los Zetas. Once Cárdenas consolidated his position and supremacy, he expanded the responsibilities of Los Zetas, and as years passed, they became much more important for the Gulf Cartel. They began to organize kidnappings; impose taxes, collect debts, and operate protection rackets; control the extortion business; securing cocaine supply and trafficking routes known as "plazas" (zones) and executing its foes, often with grotesque savagery. In response to the rising power of the Gulf Cartel, the rival Sinaloa Cartel established a heavily armed, well-trained enforcer group known as Los Negros. The group operated similar to Los Zetas, but with less complexity and success. There is a circle of experts who believe that the start of the Mexican Drug War did not begin in 2006 (when Felipe Calderón sent troops to Michoacán to stop the increasing violence), but in 2004 in the border city of Nuevo Laredo, when the Gulf Cartel and Los Zetas fought off the Sinaloa Cartel and Los Negros.