Well, popular sovereignty, or sovereignty of the peoples' rule, is the principle that the authority of a state and its government is created and sustained by the consent of its people, through their elected representatives (Rule by the People), who are the source of all political power.
Stephen Douglas's theory of popular sovereignty explains that people that live in a territory should choose whether to allow slavery or not. But Douglas's theory of popular sovereignty led to corrupted elections, violence, and political chaos.