Popular sovereignty is a political principle that is very present in the politics of the United States. This principle states that the authority of a state comes from the consent of its people through their elected representatives. In practical terms, this means that citizens are the ones who hold all power of the state and who can make decisions.
Popular sovereignty was considered a just and fair way to settle the slavery question, because this gave each state the right to decide whether to practice slavery or not. It was believed that by giving the states this right, the will of the people was respected.