One of the reasons when have such high incarceration rates is because of the three strike law. I believe that the three strikes law creates an excessive number of incarcerations. Over half of the states in the United State adhere to the three strikes law. Since the law is defined by the state government each law varies by state but the idea is always the same. The idea behind the law is to deter habitual offenders by giving them harsher sentences. The name, of course, comes from baseball and is just as it sound. Three strikes and you're out. So, the third time an offender commits a felony they receive a much harsher sentence. Most times the harsher sentence will include more time, which means there will be one more person in the prisons for longer. Also, many people go back to prison because they do not meet the rules in their parole agreements.
The second reason I believe our incarceration rates are so high, is due to our extremely firm stance on drug offenses. In 1971, President Nixon declared a War on Drugs and you still hear that phrase thrown around quite often today. Today politicians seem to be on one side or the other with no in-between. The politicians either feel that they should put a lot of money into the "war on drug" or that they should back drug policy reforms. Either way, drugs are still a problem in the United States and there are still many harsh laws in place for drugs that can lead to incarceration. And anything that can lead to more incarceration also leads to higher incarceration rates.
The third reason I believe incarceration rates are high relates back to my ideas on theories of deviancy. I take the stand that it is mostly nurture that is responsible for deviancy so I believe that the environment in which people live in the United States. When a person grows up in an area where crime is how they have learned to live, they learn to model these criminal behaviors in their own time of need.