I suspect that most of the gun violence in the United States is tied up with the trade in illegal drugs. I have never seen any statistics that support this view, it is more like a deduction from what is NOT being said.
Supposedly there was a big drop in violent crime from the 1970's to the 1990's. A number of reasons have been put forth to explain this. One of my favorites is from the book "Freakonomics". To put it in a nutshell, the author tied this drop in crime to the Row-versus-Wade decision regarding abortion back in 1973. Women were no longer forced to deliver children they did not want, so there were fewer unwanted children growing up to become violent criminals.
Another explanation I heard recently attribute the drop in crime to the Clean Air Act, passed about the same time. This act banned the use of lead in gasoline, so people were not as exposed to as much lead, and did not suffer as much brain damage, so they grew up to become proper citizens instead of muggers. I find this explanation a bit thin, but there might be some truth to it.
Then there is the official party line and that is that Rudy Giuliani and New York City Police Department arrested all the criminals and locked them up. This obviously only applies to New York City, but you can substitute your local law and order spokesman and your local police for any other place in the country. (I only pick on Rudy because people I know tell me that he deserves it.) This explanation rates as a fairy tale.
Now I have my explanation. I am sure other people have said it before, but up till now it has not been able to penetrate my brain. Crime has gotten organized. Back in the 60's there was a big expansion in the use of illegal drugs for recreational (or perhaps self-medicating) purposes. Marijuana become prevalent. Cocaine followed on and became a new import industry. All this new business upset the old established order in the existing crime syndicates, and it took 20 years for it to all to shake out and for new leaders in crime to bring organization to these illegal enterprises. With organization comes rules and enforcment. With rules and enforcement you get stability.
I have no evidence, all I have is the scuttlebutt I pick up from watching too many episodes of "Law & Order", and my own intuition.
6 hours ago