Against this backdrop many historians have come to believe that the conflict involving Missouri, the debates and compromise that followed, planted the seeds of moral, political and religious division which ultimately led to the Civil War thirty years later. In February 1819, the slavery issue in the United States was dramatically brought to everyone's attention. People were awakened to the gravity of the issue. The ensuing debate, passionate and explosive, frightened those who read about it in the newspapers. Thomas Jefferson, living in retirement at Monticello, later wrote to John Holmes of Massachusetts: "this momentous question, like a fire-bell in the night, awakened and filled me with terror. I considered it at once as the knell of the Union." He added, "I regret that I am now to die in the belief, that the useless sacrifice of themselves by the generation of 1776, to acquire self-government and happiness to their country, is to be thrown away by the unwise and unworthy passions of their sons, and that my only consolation is to be, that I live not to weep over it."
Before this time the public had paid little attention to the question of slavery. Yet, in 1819 a bill was presented to the House of Representatives that authorized Missouri’s request to join the Union and allowed it to draw up a constitution for statehood. Because slavery was already lawful in the territory and approximately more than 2000 slaves were already living in the state, many people took it for granted that Missouri would enter the Union as a slave state. Congressman James Tallmadge of New York, however, introduced an amendment to the bill. He moved that no more slaves be brought into the new state and also moved that all children born of slaves in Missouri after the state's admission should be free at the age of 25. The cry against the South’s ‘peculiar institution’ had grown louder throughout the years and now the debate was in full swing. In session with the House of Representatives, Representative Livermore from New Hampshire asked “How long will the desire for wealth render us blind to the sin of holding the bodies and souls of our fellow men in chains?”
Tallmadge’s amendment passed in the House of Representatives but the Senate, however, passed its own version of Missouri’s statehood request which included no restrictions on the institution of slavery. The task had now changed into forming a compromise between the House and Senate however the session was adjourned with no resolution. It was decided to discuss this issue at a later date. The congressional session met again in 1820, yet it was still clear that there would be no agreement regarding Tallmadge’s amendment and the Senate’s adaptation of Missouri’s request. While the legislators argued over the issue at hand, an opportunity arose with a new request for statehood from the Northern territory of Maine. With this request, two states, one free and one with slavery, could be admitted without altering the balance of power in existence. Nonetheless, the difficulty still remained, since part of Missouri’s territory was north of the Ohio River. Therefore, Senator Jesse Thomas presented a compromised bill that included the provisions of the Northwest Ordinance, 1787. This conciliated legislation was named the Thomas Proviso, and is primarily referred to as the Missouri Compromise of 1820. The provisions were as follows: (1) ‘Admit Missouri as a slave state in accordance with the initial request for statehood’. (2) ‘Approve the application for statehood of Maine as a free state’. (3) ‘Define the territories in the Louisiana Purchase, which henceforth would be free and slave’.
The 1820 Missouri Compromise marked a distinct era in the political atmosphere of the country. It made a profound impression on the minds of the population throughout the Union which set the scene for the eventual abolition of slavery. Suddenly, without warning, the North and the South, the free States and the slave States, found themselves arrayed against each other in violent and absorbing conflict. During the period between the adoption of the Federal Constitution and the admission of Missouri, there had been a great change in the Southern mind, both as to the moral and the economic aspects of slavery. The South was not going to let slavery be abolished as it now, more than ever, heavily relied on the institution for the production of its most highly sought crop, cotton. This revolution of opinion was stimulated by the invention of the gin and now the country was exporting three hundred thousand bales each year. However, this highly profitable way of life occurred in areas that were so hot and humid that outdoor labour was undesirable by the white race and therefore slaves were essential.
Such was the Missouri Compromise, that its agitation in Congress was like the opening of a foul ulcer, the beginning of that domineering, impertinent, ill-timed, vociferous and vituperative opposition which has ever since been the leading characteristic of the abolition movement. The opponents of slavery were encouraged by the more definitive roll for the Federal government in controlling the activities of individual states. Southern representatives, however, saw it as an encroachment upon the sovereignty of individual states. There would no longer be a status quo on the matter of slavery. Slavery was allowed in Missouri, but abolitionists succeeded in drawing a line of demarcation were slavery would not be allowed, which was latitude thirty-six degrees, thirty minutes. More importantly this line of demarcation applied to all future requests for statehood. (See Appendix 1) The "settlement" of Missouri in Congress seemed to be merely the signal for its agitation among the non-slave holding States. Fanatics sprang up like mushrooms, and, "in the name of God," proclaimed the enormity of slavery and eternal damnation to all who indulged in the wicked luxury.
While on the surface one could argue that the Missouri Compromise resolved the potential crisis with regards to conflicts of opinion on slavery, in actuality it created the foundation for the abolition of slavery forty years later. It emphasised divisions within the Senate (i.e. balance of power), it brought confrontations of the North vs. South (House of Representatives), it made Federal vs. State (i.e. interfering in the drafting of the Missouri Constitution), it acquired attention of the public on the issue of slavery (i.e. the debate lasted for two years) and finally it clearly marked new territories above latitude thirty-six degrees, thirty minutes, as free states. The abolitionists were unsatisfied that Missouri and other states south could be admitted as slave states, while the slavery advocates still wanted slavery to be expanded north if the need be. The anti-slavery movement, fuelled by the Missouri Compromise, kept pressure on both the South and Washington following 1820, regarding the removal of slavery from the Union, and thus perpetuated the soon to be explosive issue of abolition and the ultimate confrontation of the Kansas-Nebraska Act, followed by Civil War.