Mexico experienced its most violent year in 2017 with more than 25,000 murders, official figures suggest. It is the highest annual tally since modern records began. Organised crime accounted for nearly three-quarters of those murders.
While Mexican President Enrique Peña Nieto and his predecessor in office, Felipe Calderón, have both waged war against criminal gangs for more than a decade, it has shown little result.
A number of major cartel leaders have been arrested or killed but instead of driving homicide figures down, the crackdown on cartels has led to the fragmentation of existing cartels and the creation of new drug-trafficking gangs.
This timeline summarises the key events involving four major gangs - the Sinaloa, Juárez, Tijuana and Gulf cartels - from the beginning of Mr Calderón's presidency to the present.