National Southwest Border Counternarcotics Strategy

Drug trafficking across the Southwest border remains an acute threat to our homeland security and one of the top drug control priorities for the United States. Mexican drug trafficking organizations have come to dominate the illegal drug supply chain, taking ownership of drug shipments after they depart South America and overseeing their transportation to market and distribution throughout the United States. It is now estimated that 90 percent of the cocaine that is destined for U.S. markets transits the Mexico/Central America corridor. Mexico is the primary foreign source of marijuana and methamphetamine destined for U.S. markets and is also a source and transit country for heroin. Mexican drug trafficking organizations dominate the U.S. drug trade from within, overseeing drug distribution in more than 230 U.S. cities. These organizations also control the southbound flow of other forms of drug related contraband, such as bulk currency and illegal weapons.

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http://www.whitehousedrugpolicy.gov/publications/swb_counternarcotics_strategy09/swb_counternarcotics_strategy09.pdf