To get an idea of the long-running drug wars in Mexico, bone up on your Spanish (or let Google Translate do most of the work) and take a gander at El Blog del Narco. It is grisly and unpleasant, but so is reality in general.
The U.S. happens to be highly involved in Mexico's drug wars -- if it's not trafficking and then promptly losing semi-automatic weaponry in a failed weapons-tracking program, then it's funding the Mexican government to the tune of billions of dollars per year to help combat the ever-powerful drug cartels. Seriously, these guys DO NOT fuck around.
Meanwhile, patriotic Americans are no doubt worried about what seems to be a disturbing turn of events for them -- seeing a foreign nation staging military operations on their soil, nevermind these guys are headed straight back to Mexico to fight what seems to be a losing battle. I wonder if Gov. Goodhair knew about this. I wonder what the Teabaggers would do to Obama when they get wind of this.