What was the Nullification Crisis?

The Nullification Crisis was a sectional crisis during the presidency of Andrew Jackson created by the Ordinance of Nullification, an attempt by the state of South Carolina to nullify a federal law passed by the United States Congress. The highly protective Tariff of 1828 (also called the "Tariff of Abominations") was enacted into law in 1828 during the presidency of John Quincy Adams. Opposed in the South and parts of New England, the expectation of the tariff's opponents was that with the election of Jackson the tariff would be significantly reduced.
President Andrew Jackson was prepared to use troops to enforce federal laws, because South Carolina was making a threat that they would secede from the United States.