Slavery had been prohibited in the Northwest Territory since 1787, the second-most-important decision (after the Declaration of Independence) taken by the Continental Congress in the years between 1774 and the adoption of the Constitution in 1789. For reasons that we will go into at the proper time, this ordinance set important precedents, deciding the manner in which the new government was going to organize territories held in common. But for the moment, we confine ourselves to the results of the decision to ban slavery, which, as stated, actually predated the Constitution. (The act was reaffirmed by the first Congress.)
The Northwest Territory was the great triangle of land between the Ohio River, the Mississippi River, and the Great Lakes. The first territory owned by the general government rather than by an individual state, it was also the first territory in which slavery was prohibited from the outset. We know Jefferson’s response to the sudden surfacing of the slavery issue as a regional rather than as a national problem. It is well to remember that Jefferson had as much to do with the Northwest Ordinance’s prohibition of slavery as any man living. But he hadn’t foreseen how his precedent was going to morph until it threatened civil war.
Until 1820, the nation’s growth was incremental and non-divisive. The original 13 states had been joined by Vermont (1791), Kentucky (1792), Tennessee (1796), Ohio (1803), Louisiana (1812), Indiana (1816), Mississippi (1817), Illinois (1818), and Alabama (1819). Orderly, peaceful and logical. As new territory achieved a certain minimal population, it petitioned for admission, northwestern and southwestern states coming in more or less together. By 1820, the slave-holding and non-slave-holding states numbered eleven each.
But in 1819, the territory of Missouri applied for admission to the Union as a slave state. Missouri, like Louisiana (which had been a state for seven years), lay west of the Mississippi River, and thus was not part of the territory covered by the Northwest Ordinance.
Representative James Tallmadge, Jr., of New York offered two amendments to the Missouri statehood bill, prohibiting further importation of slaves into Missouri and requiring gradual emancipation for slaves already there. The amendments passed (along regional lines) in the House, but failed in the evenly divided Senate. This began a solid year of Congressional debate on the issue. Northerners argued that Congress had the power to prohibit slavery in a new state. Southerners said that new states had the same freedom to choose slavery as the original thirteen had had.
The slave states were already outnumbered in the House and clearly destined to be ever more outnumbered (as few emigrants chose to move to territory where they would have to compete with slave labor). They determined to keep a de facto veto power over federal legislation by maintaining parity in the Senate. The free states, meanwhile, were irritated by the constitutional provision that each male slave be counted as 60% of a man for the purposes of congressional representation, even though they were considered property otherwise. The North considered this constitutionally mandated over-representation of slave states, which it was. The admission of new slave states would make the situation worse.
Finally, the detached part of Massachusetts known as the District of Maine requested statehood. Speaker of the House Henry Clay demanded that Missouri be admitted alongside Maine, which struck his fellow representatives as a way out of their dilemma. The final compromise line was set at 36 degrees, 30 minutes latitude. Any part of the Louisiana Purchase territory below the line was to be open to slavery, and anything above it – with the exception of the state of Missouri – was to be free. The Compromise passed the Senate on March 2, 1820, and the House on February 26, 1821.
Clay’s part in the Missouri Compromise earned him the title of “Great Pacificator.” Following this pairing formula, six more states entered the Union – Arkansas, Michigan, Florida, Texas, Iowa and Wisconsin – entering, like the animals on Noah’s Ark, two by two, until in 1850 California finally overturned the balance.
In hindsight, perhaps it was a mistake to draw a line in the sand, as Jefferson saw right away. But it is the nature of politics to seek the quick fix, the easy way out, and let the future take care of itself. And perhaps the 36-30 line seemed a logical extension of the border formed by the Ohio. The Compromise did result in Congress excluding slavery from national territory, for the first time since the Northwest Ordinance. And Lincoln himself, as shrewd and thoughtful a political observer as ever lived, said that the Missouri Compromise line preserved the peace for 30 years and would have continued to do so had not Kansas-Nebraska destroyed it. Perhaps the best that can be said of the compromise is that it was the work of fallible but patriotic men, and it bought time.