Final answer:
The Missouri Compromise resulted in Missouri joining the Union as a slave state and Maine joining as a free state while setting the 36° 30' parallel as the boundary for the expansion of slavery in the West.
Step-by-step explanation:
One effect of the Missouri Compromise was that Missouri entered the Union as a slave state, and Maine entered as a free state. This agreement was reached in 1820 and was a critical step toward maintaining a balance between slave and free states. The Missouri Compromise also established the 36° 30' parallel as the northern limit for slavery in the Louisiana Purchase territory, north of which slavery was banned, except for in Missouri.