The Mexican government has a bought and paid for president. It goes downhill from there. The cartels have more money than the Mexican govt. so who is in charge?There are hundreds of millions of black market military-grade firearms circulating throughout Central and South America. The Cartels can buy anything they want. The region has been rife with insurgencies, wars, revolutions, cartel violence from Venezuela up to the Texas border for the last half-century. The Russians, the Cubans, the North Koreans, the Chinese, the Iranians have all contributed to the flow of weapons in much higher volumes than the trickle coming from the US.
The Mexican government is infested with "paid employees" of the cartels and always looking to blame the US for its epic failure at internal security. With some justification it can blame Americans and Europeans as the consumer base for narcotics, but it's been powerless to shut down the sources.