When the government assassinated the head of the cartels, the cartels always have second in command. Since there is more smaller cartels now to avoid getting caught, violence has risen an all time high because of supply and demand. When United States passed prohibition, people began purchasing and selling alcohol in the black market. The mafia took power because of prohibition. The same is happening in Mexico.
The assassination of the heads of cartels only served to carve the cartels up into smaller organizations. As each new cartel now has to compete with one another, as well as being more likely to be run by men willing to anything and be willing to die to acquire power, it caused an explosion in violence. The country has suffered horribly due to its own policies.
Yes, in response to the war, cartels have grown even more violent. There are now numerous acts of violence made to scare the population like hanging people on highways and murdering reporters to make their point. The drug cartels are so powerful they are able to act without fear of repercussions.
The drug cartels became much more violent and drugs are still being sold, at an alarming rate. American citizens who rely on the Mexican drugs just make it worse by causing an even greater demand for the drugs. So many people have died in Mexico due to the drug cartels and the violence associated with it.