Which of the following had the greatest impact on the institution of slavery in the United States in the first quarter of the nineteenth century

In 1820, the Missouri Compromise had attempted to resolve this question: It had admitted Missouri to the union as a slave state and Maine as a free state, preserving the fragile balance in Congress. More important, it had stipulated that in the future, slavery would be prohibited north of the southern boundary of Missouri (the 36 º 30' parallel) in the rest of the Louisiana Purchase.