The simultaneous admission of Missouri and Maine helped maintain peace in the United States by preserving the balance of power between free and slave states in Congress. At the time, there was tension between the North and South over the issue of slavery, and the admission of Missouri as a slave state threatened to upset this delicate balance. By admitting Maine as a free state at the same time, Congress was able to maintain the status quo and prevent further conflict between the two regions. This compromise, known as the Missouri Compromise of 1820, helped to ease tensions and preserve peace in the United States for a time.
