Answer :
The proper answer is D. Manifest Destiny. It wasn't so much the belief that democracy should be spread as it was the believe that Americans were entitled to the entire continent.
I believe the answer is: D. Manifest Destiny
Manifest destiny refers to a concept which believe that American democracy had higher level of virtue compared to other civilisation and it is the duty for American settlers to spread this across the continent.
This principle became the main reason of American conflict with Soviet Union's communism during the cold war.
