Mexican drug trafficking organizations are the largest producers or traffickers of heroin, marijuana, cocaine, and methamphetamines to the United States. This paper analyses how enforcement policies on both sides of the border affect potential smuggling routes. First, we use several data sources to build a data set that connects the Mexican cartels with local gangs (suppliers) in the United States. Then we build potential drug trafficking networks for each cartel that minimize trafficking costs, including the cost of government intervention and of turf war with competing groups. Using this baseline of most efficient routes, we estimate the impact of enforcement shocks along different segments of the network. The ultimate goal is to measure how violence disseminates across alternative routes when some of the cartels are forced to share a route due to increasing seizures or policing in a particular segment.