.Every gang is essentially an underground black market organisation. As long as there are things/items that keep being banned or in short-supply, there will always be gangs. Since marijuana is a banned substance, there are gangs who make millions selling illegal marijuana. Same with cocaine where Colombian gangs have been making billions selling cocaine in the United States. It's not just about drugs. The substance could be anything. Since rice is in short-supply today because of last year's crop destruction due to natural disasters in China, India, and Vietnam (the three largest producers of rice), gangs have started forming in these countries. The governments of these countries are trying to set up a ration system, which on the other hand is an opportunity for these gangs to sell rice through back channels and black markets.