A well trained, elite squadron of ruthless men made up of the best the US and Mexico has to offer, commanded by the finest military and strategy brains of each country and under the joint direction of the presidents of both countries who are advised by intelligence operations dedicated 100% to the objective. These men would be exhaustively trained in covert operations, would have limited family associations (and would be unidentifiable in any case) and would be paid like football stars (no plato o plomo exposure). They would play by no rules and they would take no prisoners except those they wish to waterboard for information. They would systematically kill every individual identified as associated with the drug cartels, focusing on enforcers, strategists and leadership. Cooperation with the drug cartels either side of the border would be harshly punished (Plata? Luego de plomo!) . There would be great upheaval and collateral damage but ultimately it would become a question of resources. The country would continue to bleed for years but it would also be reborn. If it maintains its current direction it will die anyway.
In order to distill the effort down to the hardcore elements driving the situation in Mexico, I expect the US will also indeed need to decriminalise cannabis, if not make it legal. The US will need to tax and regulate it and control it like it did alcohol after the failed experiment of prohibition. But there are too many rich and influential people in the US who live in a sort of la-la-land who will do their utmost and make absolutely certain that decriminalisation or legalisation does not happen. Their reasons may be noble or they may be selfish, because it is hard to imagine how the widespread use of a psychoactive substance by its poplulation would improve the country's prospects of maintaining its position in the world, particularly against rapidly emerging countries in which the recreational use of drugs is not as prevalent. But there will be solutions to this, too, and those who cannot or will not see them are as much to blame for the violence in Mexico as the cartels themselves.