When the Union was formed, African negroes were held in servitude in all but two of the States. At the time of this debate, slavery had been abolished, or was on the way to ultimate extinction, in every State north of Maryland and Delaware. Climate rather than humanitarian considerations sealed the fate of slavery at the North; and climate, in the last analysis, fastened African slavery on the South. As the South became committed to the raising of a staple, and that staple cotton, the negro was regarded as an indispensable factor in plantation economy. There were far-sighted individuals, it is true, who deprecated slavery on humanitarian grounds; but they were, for the most part, citizens of border States where the profitableness of negro labor was less apparent. Even in these communities opposition to slavery was tempered by dread of what emancipation might bring in its train. The history of Santo Domingo revealed the hideous possibilities of a negro insurrection. No father of a family could contemplate with equanimity the proximity of a large body of free, semi-civilized blacks. For a time even prominent slaveholders favored the aims of the Colonization Society which proposed to deport emancipated blacks to the African coast. So late as 1820 the Governor of Virginia recommended an appropriation by the legislature for the emancipation and removal of the negroes.

Although slavery was a local institution, and regulated by state law, its existence was recognized by the Federal Convention of 1787. The arrangement which obtained under the old Confederation, whereby five slaves were to count as three whites in apportioning representation and taxes, was continued; the mutual obligation of the States to return fugitives from justice and labor was distinctly stated in the Constitution; and the slave trade was permitted to continue at least to the year 1808.

In 1793, Congress had met its constitutional obligations by enacting a law for the return of fugitive slaves; and in 1794, Congress passed an act—"the first national act against the slave trade"—which prohibited all trade in slaves from the United States to any foreign country. By the opening of the new century all the States had forbidden the importation of slaves from abroad. But in 1803, South Carolina again legalized the slave trade; and in 1805, Congress after a brief interdiction removed all restrictions upon the importation of slaves into the Louisiana Territory. The slave trade at once assumed alarming proportions. It was officially stated that between 1803 and 1807, 39,075 negroes were brought into the port of Charleston. Eighteen hundred of these unfortunate blacks were imported in American vessels. One half of the consignees of these slavers were Americans, of whom thirteen were natives of Charleston and eighty-eight of Rhode Island.

This traffic, coupled with the alarm caused by negro insurrections in the West Indies, prepared the public mind for positive action, as the year approached when Congress might constitutionally prohibit the foreign slave trade. The Act of March 2, 1807, however, only partially met the expectations of the anti-slavery people. The African slave trade was forbidden, but negroes illegally imported were to be disposed of as the legislatures of the several States should determine. There was reason to fear that the Southern States would neglect to legislate on this important matter, and that the act would be indifferently enforced. Moreover, the coastwise slave trade for purposes of sale was not interdicted, but forbidden only in vessels under forty tons burden.

That the Act of 1807 did not prevent the African slave trade was patent to every one who knew conditions in the Southern Seaboard States; but the extent of this traffic can only be surmised. During the debates on the Missouri Bill, Tallmadge stated that fourteen thousand negroes had been brought into the country within the last year, and the statement was not challenged.

When the Missouri controversy was renewed in the session of December, 1819, the number of free States equaled the number of slave States. The addition of a twenty-third State, then, would unsettle the equilibrium between the sections in the Senate. A growing antagonism based upon widely different economic and social organizations was coming to be felt—felt rather than clearly perceived and openly recognized. In the year 1800, the two sections had been nearly equal in population; in 1820, the North outnumbered the South by over half a million. This disparity in numbers had a direct political significance, for the national House of Representatives was beyond all question controlled by the delegations from the free States. No great prescience was needed to warn the South that in self-defense it must maintain the even balance of sections in the Senate. The contest for Missouri was therefore essentially "a struggle for sectional domination."

The Tallmadge amendment was passed by the House, but rejected by the Senate, after a heated debate which convinced Southern statesmen that there was a distinct anti-slavery sentiment at the North. The adjournment of Congress threw the whole controversy into the crucible of public opinion. The latent hostility of men and women with humanitarian sympathies was at once raised to white heat. Mass meetings in city, town, and county passed resolutions against the spread of slavery and the admission of more slave States. Yet it can hardly be said that the public conscience was deeply touched. The leaven of abolitionism had to work many years before it could produce results in politics.

The whole question assumed a new guise when Congress met in December, 1820. The people of Maine had held a convention and formed a constitution, and were now applying for admission as a State. Here was a free State which would offset Missouri if it were admitted as a slave State. When the House passed a bill to admit Maine, the Senate promptly attached to it, as a "rider," a bill for the admission of Missouri without any prohibition of slavery. It was to this bill that Senator Thomas, of Illinois, representing a constituency divided against itself on the subject of slavery, offered an amendment in the nature of a compromise. He would admit Missouri as a slave State, but prohibit slavery forever in the rest of the old Province of Louisiana north of 36° 30'. The Senate accepted this amendment and sent the bill to the House. Here the original Maine Bill was stripped of the rider and the Thomas amendment by large majorities. Shortly after this vigorous assertion of independence, the House passed a bill for the admission of Missouri with the prohibition of slavery. The deadlock seemed complete.

The constitutional aspects of the problem called forth some exceedingly able argumentation. Those who favored imposing a restriction upon Missouri argued, plausibly enough, that as Congress was given the power to admit new States, so it was fully warranted in exercising discretion and refusing to admit. Precedents existed for imposing restrictions. Three States carved out of the Northwest Territory had been admitted on condition that their constitutions should not be repugnant to the sixth article of the Ordinance of 1787. The State of Louisiana had been admitted under explicit conditions. It was fully competent for Congress, by virtue of its authority over Territories, to regulate all the stages in the process of framing a constitution, and then to give or to withhold its approval.

The most brilliant argument on the other side was made by William Pinkney, of Maryland. Conceding that the power of Congress was discretionary, he insisted that Congress might not exact terms which would interfere with the results to be accomplished. "What, then," he asked, "is the professed result? To admit a State into this Union. What is that Union?... An equal Union between parties equally sovereign.... It is into that Union that a new State is to come. By acceding to it the new State is placed on the same footing with the original States.... If it comes in shorn of its beams—crippled and disparaged beyond the original States—it is not into the original Union that it comes.... The first was a Union inter pares; this is a Union between disparates, between giants and a dwarf, between power and feebleness, between full proportioned sovereignties and a miserable image of power."