Which of the following represents the belief used to justify westward expansion of Americas borders in the 1800s?

A. Monroe doctrine

B. manifest Destiny

C. Adams - Onis Treaty

D. Missouri Compromise

B) Manifest Destiny represents the belief used to justify westward expansion of Americas borders in the 1800's. Manifest Destiny is defined as "In the 19th Century, was a widely held belief in the United States that American settlers were destined to expand throughout the continent."