They were not allowed to leave and so they had to stay
The main reason why the United States largely shied away from imperialism prior to 1890 was because it was still a relatively "fragile" nation with a host of its own issues to work out--such as the slavery issue that eventually led to the devastating Civil War.
9. D and 10. A. sorry I can't help you with 7
The Supreme Court and the State Courts
The allies won World War II because of the atomic bombs developed and dropped on Hiroshima and Nagasaki, Japan.