The Kansas-Nebraska Act The Kansas-Nebraska Act was passed by the U.S. Congress on May 30, 1854. It allowed people in the territories of Kansas and Nebraska to decide for themselves whether or not to allow slavery within their borders.The Act served to repeal the Missouri Compromise of 1820 which prohibited slavery north of latitude 36°30´.The Kansas-Nebraska Act infuriated many in the North who considered the Missouri Compromise to be a long-standing binding agreement. In the pro-slavery South it was strongly supported.fter the Kansas-Nebraska Act was passed, pro-slavery and anti-slavery supporters rushed in to settle Kansas to affect the outcome of the first election held there after the law went into effect.