By the Missouri Compromise, Maines admission as a ‘free’ state (1820) was yoked to Missouris admission the following year as a ‘slavery’ state. Northern representatives bitterly opposed the spread of slave-holding to the new territories; an amendment prohibited extending slave-holding north of the 36 degrees 30 minutes parallel – a demarcation presciently described by Thomas Jefferson as the ‘knell of the Union’. With Missouris admission the rest of the former Missouri Territory was reconstituted as unorganized, as was the western half of Arkansas Territory (1824). Florida was organized as a territory (1822), while the fledgling Mexican Empire inherited the enticingly debatable Spanish territory in the Southwest (1821). In 1825, a treaty was concluded with the Russian Empire, affixing the (largely notional) border between the Oregon Territory, jointly administered by the United States and Britain, at 54 degrees 40 minutes north, a demarcation that would later prove significant under the Alaska Purchase.
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