What is up with Mexico's Drug Dealers, and is all this a treat to the U.S.?

National Public Radio is doing pretty extensive coverage of the increase in violenc among the drug cartels in Mexico. They are striking fears in a lot of people's hearts, and spreading their reach into the United States.

Cartels Fueling Violence In Mexico Take Root In U.S. : NPR
From NPR's' website:
Mexican Drug Cartels In The U.S.
The presence of Mexican drug cartels in U.S. cities is expanding. Mexican cartels have long had links to marijuana-growing farms in California, and are widening their reach into the Pacific Northwest and the Eastern United States. They also are involved in producing methamphetamines in the United States. The FBI has reported that the Mexican cartels deal only in wholesale distribution in the U.S. -- and farm out street sales to various U.S. gangs. This map shows locations of cartel activity in the United States.