Popular sovereignty is the principle that the leaders of a state and its government are created and sustained by the consent of its people, who are the source of all political legitimacy.
[1] In Defensor pacis, Marsilius of Padua advocated a form of republicanism that views the people as the only legitimate source of political authority.
[2] Popular sovereignty in its modern sense is an idea that dates to the social contract school represented by Thomas Hobbes (1588–1679), John Locke (1632–1704), and Jean-Jacques Rousseau (1712–1778).
[6] In the 1850s, in the run-up to the Civil War, Northern Democrats led by Senator Lewis Cass of Michigan and Stephen A. Douglas of Illinois promoted popular sovereignty as a middle position on the slavery issue.
The federal government did not have to make the decision, and by appealing to democracy, Cass and Douglas hoped they could finesse the question of support for or opposition to slavery.
Overnight, outrage united anti-slavery forces across the North into an "anti-Nebraska" movement that soon was institutionalized as the Republican Party, with its firm commitment to stop the expansion of slavery.
Abraham Lincoln targeted popular sovereignty in the Lincoln–Douglas debates of 1858, which left Douglas in a position that alienated Southern pro-slavery Democrats, who considered him weak in his support of slavery.