Answer:
The concept of popular sovereignty implies the theory by which the citizens of a certain nation, state or city are those who have the power to decide regarding the political destinies of the territory in which they live, and that in any case the politicians, who are elected by these citizens, they must represent the will of their voters as faithfully as possible.
This concept took hold again during the debates regarding the legality of slavery in the United States in the mid-1800s, where the Democrats pushed the defense of this concept while the Whigs and later the Republicans wanted the legality of slavery to be determined by the federal Congress. Thus, in places like Kansas this situation generated confrontations between abolitionists and slavers, in the famous Bleeding Kansas.
