howdy!
the kansas-nebraska act of 1854 was opposed for multiple reasons, heres one:
extension of slavery: the act allowed the territories of kansas and nebraska to decide for themselves whether to allow slavery based on popular sovereignty. this was seen as a reversal of the missouri compromise of 1820, which had prohibited slavery north of the 36°30' latitude line in the louisiana territory. northerners opposed the idea of allowing slavery to expand into new territories.