The article accompanying this illustration by Luis Atorga offers six possible approaches to the drug violence in northern and western Mexico. A mix would probably be good, but an effort to develop Mexico's economy for the good of Mexican workers is essential.
You also should look at Richard Grabman's recent post here on why legalizing drugs is too simple-minded an answer.
And Richard has a very informative post on the gun trade and shared responsibility for it some foolishness by officials here.
In general you'd do well to read Richard's blog, The Mex Files, for very useful information and insight into Mexico from an articulate, extremely well-informed American with clear vision who lives here.