What's the cause of prison riots ?

It is impossible to ignore what has been happening in Brazil since the New Year has started. Several prison riots have already caused many prisoners' death and the police are having a hard time to quell /to stop these rebellions,aren't they ?

Have you read about the prisoners and gangs' warfare? Why has the tension raised inside their cells? Where have the prisoners been killed? How are the authorities reacting to these violent riots? Is it a recent or a long term problem in Brazil?

http://www.macmillandictionary.com/dictionary/british/warfare

http://www.macmillandictionary.com/dictionary/british/riot_1

http://www.macmillandictionary.com/dictionary/british/quell 

The question that everybody asks then is: What's the cause?

In fact, there is not only one reason or cause to explain such violent riots.

If you click on the links below, you are going to read more information about these Brazilian riots, ok?

http://www.bbc.com/news/world-latin-america-38534769

https://www.thestar.com/news/world/2017/01/02/prison-riot-in-brazil-leaves-at-least-60-inmates-dead.html

http://edition.cnn.com/2017/01/14/americas/brazil-prison-riot/