The Louisiana Purchase of 1803 more than doubled the size of the United States, and included the area of the future state of Missouri. As settlers began to move into Missouri, the balance of free and slave states shifted. In 1819, Missouri applied to join the Union as a slave state, which would upset the balance in Congress. This crisis was resolved by the Missouri Compromise. The compromise allowed Missouri to enter as a slave state, while Maine entered as a free state, thus preserving the balance of power. The compromise also established a boundary dividing the Louisiana Territory between free and slave territory. North of this line, slavery was prohibited; south of this line, it was allowed. The Missouri Compromise was a temporary solution to a divisive issue, but it would later be overturned by the Supreme Court in the Dred Scott decision.