How did missouri compromise (1820) challenge state rights

In 1820, amid growing sectional tensions over the issue of slavery, the U. S. Congress passed a law that admitted Missouri to the Union as a slave state and Maine as a free state, while banning slavery from the remaining Louisiana Purchase lands located north of the 36º 30' parallel.

well, it was a very difficult decision because passed a bill granting Missouri statehood as a slave state under the condition that slavery was to be forever prohibited in the rest of the Louisiana Purchase north of the 36th parallel, which runs approximately along the southern border of Missouri.