In Mexico the politicians are corrupt, and police are corrupt, and the drug cartels are just what they are. With nothing to keep them in check they probably have more influence than the other two.
What I’m talking about predates the Drug Cartels. They are a proverbial secondary infection after the government that managed to piss away the opportunities that post-colonial Mexican had (along with being a symptom of a market full of stupid hippies and addicts in their northern neighbor who are, not coincidentally, now managing to piss away some of our own opportunities and will, if left unchecked, finally cause the nation to descend into madness, futility and bankruptcy). Had Mexico City emulated the United States or even Great Britian, rather than continentals, they would probably have fared much better (just as Botswana has done: a country with none of Mexico’s advantages, incidentally).
The Drug Cartels are then like an infection that comes along because the immune system is already badly compromised.