What principle was john adams referring to in this statement?

John Adams (1735–1826), who served as the first vice president of the United States and then as its second President, also influenced the development of constitutional government through his political writings and thought.

Explanation:

The Mexican-American war (1846-1848) changed the slavery debate. It almost doubled the size of the United States and began a debate, between Northerners and Southerners, over what to do with the newly acquired land.