Why did southern whites feel threatened by the Mossouri Compromise?

Southern whites felt threatened by the Missouri Compromise because it established a geographic boundary for slavery in the newly acquired territories, limiting its expansion. By admitting Missouri as a slave state while Maine was admitted as a free state, the compromise maintained a delicate balance in Congress but also set a precedent for restricting slavery's growth. This raised fears among southern leaders that the increasing number of free states would eventually lead to a political and economic disadvantage for the South, jeopardizing their way of life and the institution of slavery itself.