In 1819, when Missouri petitioned Congress to allow it to start drafting a constitution and seek admission as a state, Representative James Tallmadge, Jr., of New York offered an amendment to the Missouri enabling act to prohibit slavery in the new state. The Tallmadge Amendment set off a fierce debate about the future of slavery and Congress's power to stem its expansion into new states.
The Continental Congress limited slavery's territorial expansion in 1787 when it outlawed slavery north of the Ohio River with the Northwest Ordinance. The proposal that Congress ban slavery as a condition for admitting a new state, however, outraged many members of Congress, particularly southerners.
Southern senators argued that banning slavery from Missouri amounted to destroying the equality of states. Senator James Barbour of Virginia, for example, protested that the ban "seeks to fix on Missouri the badge of inequality and degradation," a step "repugnant to the . . . letter and spirit of the Constitution." Barbour argued that it was the Senate's duty to preserve state equality. "The crisis has arrived," he stated, "contemplated by the framers of the Constitution, and to guard against whose effects was the principle object of the creation of the Senate." Pennsylvania senator Johnathan Roberts correctly pointed out that the Constitution did not in fact promise new states would be admitted "on the footing of the original States." Senator David Morril of New Hampshire emphasized that "We are not legislating for Missouri alone, but for the highest interest of the nation."
The heated debate over the Missouri Crisis lasted for more than a year, ending with a compromise decision designed to maintain a balance not only in the nation but in the Senate over the issue of slavery. Congress agreed to admit Missouri without a restriction on slavery, to admit Maine as a free state, and to prohibit slavery in the territories north of the 36° 30' parallel.
The Missouri Compromise placed the Senate at the center of debate for the next several decades. As northern populations grew, bringing more representatives from those states, southern strength waned in the House of Representatives, leaving to the Senate, where every state has an equal voice, the burden of maintaining sectional balance in the hope of avoiding civil war. That balance would be continually threatened as lawmakers pursued a policy of Manifest Destiny, pushing the nation's boundaries ever westward. Over the next two decades, Congress admitted states in pairs, slave and free, in order to maintain the balance established in 1820. Ultimately, the organization of the southwestern territory gained from the war with Mexico, and the admission of California in 1850, upended the balance of power and set the nation more firmly on its path to disunion.
