There are underlaying problems like the war on drugs but the cartels in Mexico are more than just drug businesses now. They branched out into other illegal and legal industries then enforces things with paramilitary like gangs.
Now the US going in probably isn't a good idea but mostly because Mexico isn't really asking for us to. Mexico isn't really planning on a peaceful approach either. We are talking about people who use extreme violence and terrorism to achieve their goals and maintain power.