The Los Zetas Cartel changed the game in the Mexican War on Drugs. From the mid-2000s, they introduced an unprecedented level of violence – paramilitary-style executions, beheadings, bodies hung from bridges.

But this was not simply psychopathic violence. These were special forces soldiers from the Mexican military – who had received specialized training from the US Army – who had defected, and used their training to become the most feared drugs cartel in Central America.

Watch more from this series:

The Opioid Crisis Sweeping Africa

Will Robots Be the Drug Dealers of the Future?

How to Legalize Weed

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