Congress was compelled to establish a policy to guide the growing of slavery into the new western territory. Missouri’s application for being recognized as a slave state sparked a bitter national discussion. In addition to the deeper issue constitute by the growth of slavery, the addition of pro-slavery Missouri legislators would give the pro-slavery faction a Congressional majority.
Congress reached a series of agreements that became known as the Missouri Compromise. Missouri was admitted as a slave state and Maine was admitted as a free state, maintaining the Congressional balance. A line was also drawn through the unincorporated western territories along the 36°30' parallel, dividing north and south as free and slave.
Thomas Jefferson, hearing the deal, “considered it at once as the knell of the Union. It is hushed indeed for the moment. But this is a reprieve only, not a final sentence. A geographical line, coinciding with a marked principle, moral and political, once conceived and held up to the angry passions of men, will never be destroyed; and every new irritation will mark it deeper and deeper.”