1820 marked the first “official” compromise over the issue of slavery since the Constitutional Convention in 1783. The Founders had initially added provisions within the Constitution to address aspects of slavery to convince southern states to side with the new government, however, they also intended to phase it out in the coming decades. With the signing of the Constitution there were seven free states and six slave states.
As new states were admitted, a balance was struck between slave and free. The first two additions were Vermont (free, taken from a portion of New Hampshire) and Kentucky (slave), then Ohio (free) and Tennessee (slave), then Louisiana (slave, finally brought equal numbers for free and slave), then Indiana (free) and Mississippi (slave), and finally Alabama (slave) and Illinois (free). In 1819 the ratio was 11 free states and 11 slave states. This allowed equal representation within the Senate and provided a certain degree of peace for the time being.
This all changed when the Missouri Territory petitioned to be admitted as a slave state in 1820. While the acquisition of the Louisiana Territory provided significantly more land for new free states, none of these territories had the numbers to apply for statehood at the time. Many Northern states were concerned that the addition of Missouri would give slave states an advantage that they could use to permanently legalize slavery for the foreseeable future.
To address this problem, a compromise was announced that would limit the creation of slave states in any future sections of the Louisiana Territory north of the 36 30’ parallel. At this same time, Maine, formally a part of Massachusetts, petitioned for statehood as well. This provided the opportunity for balance once again. The Missouri Compromise was passed in 1820 thanks in large part to the efforts of Speaker of the House Henry Clay. Clay worked tirelessly to pass the bill with as much bipartisan support as possible. Two bills were passed, the first setting the 36 30’ line and admitting Maine as a free state, and the second admitting Missouri as a slave state.
The Missouri Compromise set a precedent for future conflict. The Compromise of 1850 admitted California as a free state while allowing slave states to form from the New Mexico territory. The Kansas-Nebraska Act of 1854 set new lines for slave states, allowing the Kansas and Nebraska territories to be established as free or slave depending on the vote of its citizens, in effect abolishing the 36 30’ provision of the Missouri Compromise. Ultimately the U.S. could not rely on compromises and eventually went to war over the issue of slavery in 1861.