As part of the Missouri Compromise, Missouri was admitted to the Union as a slave state, and Maine was admitted as a free state. This was done purposely in order to

A.
make sure the abolitionists of Maine and other New England states were satisfied.
B.
maintain an equal balance of free states and slaves states within the country.
C.
keep slavery to the west of the Mississippi River and north of Oklahoma.
D.
ensure that slavery was outlawed in any part of the Louisiana Territory.

B. maintain an equal balance of free states and slave states within the country.