Mexico's two pre-eminent cartels — the Sinaloa Federation in the west and Los Zetas in the east — progressively brought smaller and geographically disparate groups under their influence throughout 2011. By the beginning of 2012, Sinaloa had begun to rely on its affiliate groups, most notably the Cartel de Jalisco Nueva Generacion (CJNG), to combat its Zetas rivals, while Los Zetas more frequently worked with local groups with knowledge of and contacts in their regions to combat Sinaloa. This trend has largely continued through the first quarter of 2012. The polarity of Mexico's criminal landscape in some ways is a byproduct of the country's geography, which lends itself to distinct trafficking corridors that run parallel on either side of the country.