How did the Missouri Compromise of 1820 contribute to the Southern secession?

Its failure in keeping the resolution of the 36th parallel line.

Explanation:

The Missouri Compromise attempted to reduce the conflict between the North and South arising over the issue of slavery states and free states. However, the drawing of a line at the 36th parallel which determined free and slavery states created sectional tension. The states above the line were made to prohibit slavery and the states below the line were allowed to expand the practice of slavery. This division ultimately contributed to the Southern succession from the Union as the war with Mexico gave rise to new territories like California, Utah and New Mexico but the resolution of the compromise did not apply on them. Instead California was made into a free state and states like Utah and New Mexico were given the right to either join the free state or slavery state through the resolution called Wilmot Proviso. This resolution was greatly criticized by the South.

The Missouri Compromise of 1820 contribute to the Southern secession is discussed below in details.

Explanation:

Missouri Compromise of 1820

Maine and Missouri applied to join the Union. The Missouri compromise allowed both to become the part of the Union, Maine as a free state and Missouri as a Slave state.

Louisiana territory north of the southern boundary of Missouri would be free. Permitted slave masters to pursue fled slaves in the North.

Southerners were outraged that congress gave itself the authority to make laws about slavery. the North did not want slavery but the South did and when the congress allowed another state to be a slave state the north was angered.