Kansas-Nebraska Act 1854 (jan 1, 1854 – jan 1, 0)
Stephen Douglas preserved a bill to divide the territory into Nebraska in the North and Kansas in the South, where both would have popular sovereignty. The bill became a law and repealed the Missouri Compromise. This act proved that the general population had very strong opinions either for or against the bill mirroring the strong views that would carry on leading up to the Civil War.
Added to timeline:
Causes of the Civil War