The post above has the two schools of thought about prison violence very clearly laid out though I would add that gangs in prison have a strong presence also. I have to add to this question as I am a volunteer crisis counselor in a county jail which means I am called when a prisoner requests someone to talk to when they are in crisis. I sometimes see them in a padded cell or with them wearing cuffs, but always distressed and often suicidal. Many of them have no one who cares whether they live or die which is many times their biggest problem. There are reasons why they don't, but like any other human being, they want someone who cares or who will visit them. I've also taught in a juvenile prison and in a federal adult prison. Many of them said that the number one reason they left school is that "no one cared" which again is that human need to be cared about. As a teacher, I don't agree with the "no one cared" because I often see teachers reach out and are rejected. I find that their feelings of abandonment or being alone in the world add to the despair and violence.
There are at least two different schools of thought on this.
One, shown in the link below, holds that the way to reduce prison violence is to be tougher on prisoners. If prisoners know that violence will be punished severely, they will not be so likely to be violent.
A second school of thought holds that prisoners should be treated better. If prisons were less crowded, for example, there would be less friction between inmates. If prisoners had more things to do (like take classes or participate in sports programs), they would have less time on their hands and would also be motivated to stay peaceful so they would be able to remain eligible for those programs.
We could release all the non-violent drug offenders across the country. In some states, someone who merely is in possession of marijuana can have a life sentence, if caught 3 times. So, in essence, they can get life for 3 joints. Our jails are overcrowded with non-violent drug offenders. By the time they come out, they have a much higher chance of being jaded and more violent.
The US has the highest rate of incarceration in the world! We can easily bad mouth China for its civil rights violations, but they have over 1.3 billion people and 1.6 million incarcerated. Meanwhile we have 2.4 million people in jails in this country. That's 800 million more inmates than China with 1 billion less people.