In 1820, slave-holding states still held a majority in the US Senate. The majority in part derived from the ‘three-fifths’ rule, whereby slaves counted for 60 per cent of free persons in determining representation per state. This precarious advantage was now threatened by the ‘free’ District of Maine’s application for statehood. As price for its recognition, the slave-holding states demanded Missouri’s admission with a constitution permitting slavery. After heated debate, the Compromise was enacted, with a further proviso: the USA’s remaining western territories would be ‘free, north of the 36° 30’ latitude line in the Louisiana territories. Effectively, this left the Arkansas territory, to the south of the line, within the slave-holding orbit. Thomas Jefferson saw the Compromise as sounding the ‘Knell of the Union’, by formally recognizing the North-South divide. It would be abrogated by the Kansas–Nebraska Act of 1854, thereby precipitating the descent to Civil War.
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