The Kansas-Nebraska act of 1854 created a popular sovereignty in the Kansas and Nebraska territories west of Missouri, thus nullified the Missouri compromise and reopening the issue of slavery into the states. The act, proposed by Stephen A. Douglas of Illinois, was controversial because it handled slavery. The Missouri compromise of 1850 stated simply that Missouri and only Missouri could be a slave state even though it was above the central border across American that divided the slave and free states.

The Kansas-Nebraska Act void and replaced the Missouri compromise by making the territory west of Missouri into two separate states. Each of the states were allowed to vote their own decision as to whether or not slavery was allowed and/or approved by the state; this was known as popular sovereignty.

Because slavery was now up for vote, the chance of slavery becoming legal was available once again above...