The Missouri Compromise of 1820 was passed by the pro-slavery and anti-slavery factions within the United States Congress, who had reached a boiling point thanks to Missouri's request to enter the Union as a slave state in 1819. If this request was granted, the delicate slave and free state balance would be uneven, thus, the Missouri Compromise was taken into affect as a peacekeeping measure to ease the tension between the pro and anti-slavery elements. This compromise granted Missouri's wish to enter as a slave state, but also admitted Maine as a free state into the Union, therefore, the number of free and slave states stayed even. The Missouri Compromise stayed in affect until it was interrupted by the Kansas-Nebraska Act that went into affect in 1854.