Final answer:
The correct term for America growing in size, often associated with Manifest Destiny, is the A) Westward Expansion Era, which contributed to sectional tensions over slavery.
Step-by-step explanation:
When examining the comparison between Americans disagreeing over different issues, such as slavery, which is associated with Sectionalism, and America growing in size, the correct term to use would be the A) Westward Expansion Era.
This period was marked by a belief in Manifest Destiny and included significant events like the Louisiana Purchase, which doubled the nation's size, and the acquisition of territories after the Mexican-American War.
These expansions caused increased disputes over whether new states would be free or slave states, contributing to the tensions that led to the Civil War.