Over the past fifty years, to earn the median wage, a Mexican has had to sell an average of 700 grams of marijuana, 18 grams of heroin, or 66 grams of cocaine on the U.S. streets. It amounts to weed weighing two cans of soup, coke weighing a tennis ball, or smack weighing just three U.S. quarters. And this is only the average. During the economic collapse of the mid-1980s, it took only 280 grams of marijuana and 4.8 grams of heroin to make the annual wage. You could earn as much growing a single marijuana plant or a window box of poppies as driving a cab for a year.
Up to the 1970s, violence was rarely employed to sort out disputes between drug traffickers. The trade was relatively peaceful. Cooperation was the rule. Deep ties of blood, marriage, friendship, and neighborhood, which linked many of the traffickers, prevented the frequent use of force. In general, so did the local protection rackets. Both state governors and state cops were keen to avoid conflicts that risked exposing their own ties to the traffickers.
This changed because sometimes the later state authorities sought to institute their own protection rackets, using force toward that end. Many of the gangs sought to extend their turf beyond drugs to other commercial areas, also leading to conflict. Finally, the U.S.-led war on drugs induced a form of Mexican aggressive counternarcotics policing that bred conflict as well.
Overall this is a good book about a hard to research topic.