[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] This dissertation examines the career of James Sidney Rollins, a free-soil slave owning politician and lawyer in Missouri, to garner a better understanding of the politics of slavery in the years surrounding the Civil War. Rollins, like many Border State slaveholders, staked out a moderate public position on slavery and decried abolitionists and fire-eating proslavery demagogues as extremists who sought to destroy the Union. By the middle of the 1850s, Missourians recognized that significant demographic shifts in their state brought about by railroad construction and large waves of immigration from Germany, Ireland, and northern states undermined the political and social support for the slave regime. More immediately, however, the violence and unlawfulness of the proslavery element in Kansas placed Rollins's personal beliefs, political ambition, and economic wellbeing in tension. He gradually worked to reconcile his private statements with his public positions, all while being mindful of the economic effect of emancipation would have on slave owners in Missouri. Twice elected to the House of Representatives during the Civil War, Rollins cast one of the deciding votes on the Thirteenth Amendment to the Constitution, freeing all enslaved people in the country. The story of Rollins's career fills a gap in the current historiography of Civil War emancipation. Historians who discuss emancipation tend to focus on the efforts of a small minority of radical northerners who advocated for immediate abolition, or on the work that enslaved people did to emancipate themselves as the system began to erode around them prior to and during the Civil War. Both of these perspectives are important but modern scholarship has elided the complicated efforts of the political center at the edges of slavery's reach to bring about an end to the peculiar institution. Despite harboring personal animosity or at the very least ambivalence toward slavery, Rollins found his public statements on the institution moderated by the political realities of his state. Operating within a constrained framework of what was politically feasible, Rollins helped prevent his state and the institutions within it from falling prey to proslavery extremists. Men like Rollins and his allies worked from within the slavery system to bring about its end while simultaneously ensuring states like Missouri and Kentucky maintained their invaluable connection to the United States during the war. This work also complicates the narrative that historians of slavery and capitalism tell about the continued viability of the slave labor regime during the middle of the nineteenth century. Unlike states in the deep south, Missouri failed to attract the wealthiest slave owners because a lucrative staple crop never became dominant. Hemp and tobacco served as nominal staples but could not produce the levels of wealth that the southern cotton belt witnessed. Consequently, a smaller proportion of Missourians owned slaves, and those who did, held fewer on average than in other parts of the South. The geography of Missouri, jutting out into the northern states, helped ensure that the state's economy became closely tied to the states of the north and that free labor emigrants flooded into the state. By the late 1850s Missourians on all sides of the debate on slavery's future believed that these factors were undermining slavery, a fact that cuts against the trajectory of slavery presented by the capitalism and slavery scholarship.