Stephen Douglas, one of the politicians behind the Compromise of 1850 which had declared California a free state but opened the Utah and New Mexico territory to slavery, proposed the Kansas-Nebraska Act primarily to encourage the construction of a transcontinental railroad. Yet, his proposal to organise the territories which the railroad would cross ran against the issue of slavery, an issue that Douglas had not forseen and that ultimately brought him down as a politician. The proposed act appealed to popular sovereignty, declaring that the decision of whether to open these territories to slavery would be up to their inhabitants. Yet, this vague formulation went against the Missouri Compromise which had outlawed slavery in the area from latitude 36° 30' north to the Canadian border. In exchange of their support, Southern politicians explcitly demanded that the Act repealed the Missouri Compromise and Douglas conceded the point. With the support of President Pierce, the law was approved in May 1854.
Yet, the political debate that it generated went much further than what Douglas had initially expected and contributed to a stronger division of the country between pro-slavery groups and abolitionists. This stronger division would contribute within a few years to the break up of the Union. It also led to the realignment of political allegiances with the collapse of the Whig Party, the discomfort of Northern anti-slavery Democrats and the formation of the Republican Party. The future President Abraham Lincoln denounced the Act as going against the will of the authors of the Constitution putting as it did slavery "on the high road to extension and perpetuity".