popular sovereignty, in U.S. history, doctrine under which the status of slavery in the territories was to be determined by the settlers themselves. Although the doctrine won wide support as a means of avoiding sectional conflict over the slavery issue, its meaning remained ambiguous, since proponents disagreed as to the stage of territorial development at which the decision should be made. Stephen A. Douglas, principal promoter of the doctrine, wanted the choice made at an early stage of settlement; others felt that it should be made just before each territory achieved statehood. First proposed in 1847 by Vice President George Dallas and popularized by Lewis Cass in his 1848 presidential campaign, the doctrine was incorporated in the Compromise of 1850 and four years later was an important feature of the Kansas-Nebraska Act. Douglas called it "popular sovereignty," but proslavery Southerners, who wanted slavery extended into the territories, contemptuously called it "squatter sovereignty."