The main thing which allows narco-terrorist to thrive is rampant corruption in the Mexican government which allows them to pay off and even seize control of local police, judges and the like.
I'm not saying that Northern Mexicans are immune to the corruption and bribery which is endemic in the south, but they are certainly less inclined toward it.
Put in the right leadership and enforcement and they will go with their natural inclinations toward industriousness versus their southern cousins natural inclination toward following the course of least resistance.
Case in point: Columbia, which was once a haven for narco terrorism and corruption and, sadly, with the neglect of the Obama administration may move back in that direction. Yeah, we gave them a little money during the Bush administration to help clean it up. But the results were dramatic. Even after four years of neglect under ObaMao's regime, they are still on the right path toward first world status.
And what allows them to pay off local police, judges and the like are drug-war-inflated drug profits.