In 1819–20, the question of slavery's expansion into Missouri and other western territories was a matter of fierce political debate.
Jefferson and other southerners favored the "diffusion" of slaves in the west, believing that the spread of enslaved people over a larger geographic area would improve their situation and lead more swiftly to emancipation.
Jefferson’s “fire bell in the night” letter to John Holmes, dated April 22, 1820, in which Jefferson discusses expatriation and diffusion of slaves.
Letter from Thomas Jefferson to John Holmes, April 22, 1820. Library of Congress