Monroe Doctrine and the Roosevelt Corollary

The United States has repeatedly intervened in the affairs of many Latin American countries in the past century based upon the Monroe Doctrine and the Roosevelt Corollary.
Briefly explain the two doctrines, and give an example of how each one has been applied in Central America.
Select an example of U.S. intervention in a Latin American country. Explain the reasons for the intervention and the outcome.
Was the U.S. justified in doing this in your opinion? Explain your answer.