pbEssential reading.-Steve Coll, NewYorker.comb pbA gripping, sobering account of how Mexican drug gangs have transformed into a criminal insurgency that threatens the nation's democracy and reaches across to the United States.b pThe world has watched, stunned, the bloodshed in Mexico. Forty thousand murdered since 2006 police chiefs shot within hours of taking office mass graves comparable to those of civil wars car bombs shattering storefronts headless corpses heaped in town squares. And it is all because a few Americans are getting high. Or is it part of a worldwide shadow economy that threatens Mexico's democracy The United States throws Black Hawk helicopters, DEA assistance, and lots of money at the problem. But in secret, Washington is at a loss. Who are these mysterious figures who threaten Mexico's democracy What is El Narco pEl Narco is not a gang it is a movement and an industry drawing in hundreds of thousands, from bullet-riddled barrios to marijuana-covered mountains. The