The simultaneous admissions of Missouri and Maine would help to maintain peace in the United States by creating a balance of power between the free and slave states. This would help to prevent the conflict between the North and South from escalating into a full-blown civil war. By allowing both states to join the Union, it would also help to ensure that the rights of all citizens were respected and protected. Additionally, it would help to ensure that the federal government was able to remain neutral in the conflict between the two sides.
