Senator Stephen Douglas was called "the little giant of the Senate." He was the foremost supporter of the Kansas-Nebraska Act. He strongly supported the concept that Western territories should have the right to choose on their own whether they would be free or slave states. Douglas longed to break the deadlock that existed on westward expansion, which he felt was stifling the growth of the Union. In addition, being a representative of Illinois and a heavy investor in real estate and rail stocks, Douglas knew that westward expansion in the Nebraska-Kansas area could not help but benefit him personally. Thus, the Kansas-Nebraska Act was born.

The act, which effectively overturned the Missouri Compromise, allowed each territory to decide for itself whether it wished to be a free or slave state. The general understanding was that Nebraska, lying west of free Iowa would naturally be free; but that Kansas, lying west of slave Missouri would become a slave state. The promise of another slave state enlisted strong southern support for the plan. It inflamed much of the North, however.

Despite the storm of protest that developed, the act was passed. Its passage split the Democratic party, leading to the establishment of the Republican party.