The passing of the Kansas-Nebraska act in 1854 opened up a new battlefront in the United States between those for and against the institution of slavery. Senator Stephen A. Douglas, who sponsored the bill, supported the notion of popular sovereignty; that the people who lived in a certain territory could decide by themselves whether or not to allow slavery. In so doing, he began a race between rebellious free-staters and resistant pro-slavery partisans to claim Kansas as their own, which lead to an outburst of violence that history remembers as the Bleeding of Kansas.