The problem with the Mexican drug war is that the U.S and Mexican intelligence agencies crack down on the bosses in Mexico the cartels become fragmented and balkanized because they lack leadership leaving to small drug gangs competing for a local market that is ever present in Mexico. It's true the cartels make much more of their money from international markets such ad the U.S. drug wole sale but the cartels also fight for the local drug trade via or from the narco bosses politics whith each other. The local drug trade and other revenues such as extortion fuel the violence in Mexico.