Final answer:
Congress's reaction to the proposal of admitting Missouri as a slave state in 1819 was bitterly quarrelsome, highlighting deep national division over slavery and leading to the Missouri Compromise.
Step-by-step explanation:
In 1819, when Congress received a proposal to admit Missouri as a slave state, the reaction can best be described as bitterly quarrelsome. The admission of Missouri sparked heated debates around sectional balance, the morality of slavery, and the future of the Union. The situation was so intense that it nearly tore the fabric of the nation and foreshadowed the potential for disunion and civil war. In Congress, representatives like James Tallmadge introduced measures to prohibit slavery in Missouri which were met with unanimous outrage from Southern states.
The argument escalated to such a degree that it required the formulation of the Missouri Compromise, under the guidance of Henry Clay, to calm tensions. The Compromise admitted Maine as a free state and Missouri as a slave state, with a geographical line establishing the boundaries for the future expansion of slavery.