On 22 April 1820, Thomas Jefferson had written to John Holmes, predicting that the Missouri Appeasement would eventually lead to the destruction of the USA:
…I 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 obliterated; and every new irritation will mark it deeper and deeper.