How much time do you have for the history of Mexico, including US military campaigns, trade policies and clandestine operations that none of them left the place more stable than it was before?

Any place you have the desperately poor and the obscenely rich, you're gonna have instability. Mexico being next door to the richest and most powerful country in the world has tended to exacerbate those internal tensions even worse. And when there's violence in the streets and no food on the table, people tend to gravitate towards whatever power is offering solutions to those problems, be they revolutionary leftists, or drug cartels that are more willing to throw money at you for your complicity than the official government and the wealthy city dwellers.