Final answer:
John C. Calhoun is best remembered for his defense of states' rights, the concept of a concurrent majority, and his role in the Nullification Crisis, reflecting his dedication to the interests of the South, notably in preserving slavery.
Step-by-step explanation:
As a prominent political figure, John C. Calhoun's greatest accomplishment is notably his defense of states' rights and the institution of slavery during a time when the United States was deeply divided over these issues. He is particularly known for advancing the idea of a concurrent majority, which allowed a regional minority to veto actions by a national majority, arguing that it would protect the South's interests, particularly concerning slavery.
His most substantial political maneuver was during the Nullification Crisis, where South Carolina, Calhoun's home state, sought to nullify federal tariffs, ultimately leading to the Compromise Tariff of 1833 and momentarily avoiding a deeper national crisis. Calhoun's steadfast advocacy for the South and its way of life, as well as his role in the development and defense of the region's stance on slavery, highlight his political influence and commitment to his constituency.