When the Kansas and Nebraska territories were founded, slavery was quite a big issue in the nation. Democrat Stephen Douglas proposed an act of popular sovereignty, which essentially meant that the territories decided whether or not to allow slavery. This led to the Kansas Nebraska Act, which led to a great series of disputes and controversies.
First of all, it voided the Missouri act of 1820. It stated that all states and territories that were above the Missouri-Arkansas border were non-slave states, and those below were slave states. However, both the Kansas territory and the Nebraska territory were above the border, so the should have been non-slave states. This caused much upheaval in the way of nullifying an important document.
Before the Kansas Nebraska act, the Republican party was quite scattered and not put together. However, the Kansas Nebraska Act and the spread of popular sovereignty help unite the Republican party and eventually lead to Abraham Lincoln’s eventual election into office.
Finally, it increased violence over abolition. There were several instances in which violence erupted over abolition in the colonies, a sort of pre-Civil War, if you will. this made fighting a norm, and made tensions between the north and the south even greater. Overall, the Kansas Nebraska act was one of the primary causes of the Civil War.