Los Zetas
Since 2011, Los Zetas and the Sinaloa cartel have emerged as the two main criminal syndicates in Mexico's drug war, with smaller gangs lining up on either side in a competition that now resembles a "full-scale war." A string of mass slayings have convulsed Mexico in 2011 and 2012. Many of them took place in northern states, where Los Zetas have waged a war against rival drug trafficking organizations for the control of the smuggling routes into the United States. The Los Zetas gang dates back to 1999, when deserters of the Mexican Army Special Forces joined the ranks of the Gulf Cartel. Nonetheless, the two organizations split in early 2010, and have fought for the control of the trafficking routes since then. The powerful Sinaloa Cartel, the Zetas' mortal rivals, has stood up and fought Los Zetas too. Since late April 2012, Los Zetas has been under immense pressure by the alliance between the Gulf cartel and the Sinaloa cartel. In March 2012, thirteen Los Zetas' members were killed and dismembered by the Sinaloa Cartel in a turf war; Los Zetas responded in kind, killing at least 10 members of the Sinaloa cartel in their rival's turf.