* Southern slave owners: Some Southern slave owners favored the war because they believed that the acquisition of new territory in the Southwest would provide a place to expand slavery.
* Business interests: Some business interests favored the war because they saw it as an opportunity to expand trade with Mexico.
* Manifest destiny: Many people in the United States believed in the concept of manifest destiny, which held that the United States was destined to expand its territory across the North American continent. This belief contributed to support for the Mexican-American War.