Globally 9 million people are in prison, 25% of those prisoners are in USA, why?

Because the USA is seriously messed up. A country you can own a gun and drive a car in your teens, but can't have a drink until you're over twenty. Where the right to bear arms is more important than not having children and other people murdered in schools and elsewhere. Where there's basically a tax called "tipping" that is not really a gratuity. The Monroe Doctrine?

There are many great and good things in the USA, but there's too much that is not. It has stiffled the growth of a decent and sustainable culture. The common denominator in the USA seems to be rather lacking in culture, which is why much of the rest of the world perceives the USA as brash and arrogant.

Most of USA prisoners are non-violent offenders in for frivolous reasons- pot or coke possession. The private prison industry needs guests. The math is easy.

Home of the free is not so free. The US incarcerates more people than any other country except for Russia.

Then they wonder why we all don't vote.

Because not enough people have the ability to defend themselves.