How did the Missouri Compromise relate to states rights?

The appeal to states' rights is of the most potent symbols of the American Civil War, but confusion abounds as to the historical and present meaning of this federalist principle.

The Missouri Compromise was an effort by Congress to defuse the sectional and political rivalries triggered by the request of Missouri late in 1819 for admission as a state in which slavery would be permitted. At the time, the United States contained twenty-two states, evenly divided between slave and free. Admission of Missouri as a slave state would upset that balance; it would also set a precedent for congressional acquiescence in the expansion of slavery.