John Caldwell Calhoun (March 18, 1782 – March 31, 1850) is a leading politician and political theorist from South Carolina during the first half of the 19th century.

Calhoun eloquently speaks out on every issue of his day, but often changes positions.

Calhoun begins his political career as a nationalist, modernizer, and proponent of a strong national government and protective tariffs.

After 1830, he switches to states' rights, limited government, nullification and free trade.

He is best known for his intense and original defense of slavery as something positive, his distrust of majoritarianism, and for pointing the South toward secession from the Union.

Devoted to the principle of liberty (though not for slaves) and fearful of corruption, Calhoun builds his reputation as a political theorist by his redefinition of republicanism to include approval of slavery and minority rights—with the white South the minority in question.

To protect minority rights against majority rule he calls for a "concurrent majority" whereby the minority can sometimes block offensive proposals.

Increasingly distrustful of democracy, he minimizes the role of the Second Party System in South Carolina.

Calhoun's defense of slavery becomes defunct, but his concept of concurrent majority, whereby a minority has the right to object to or even veto hostile legislation directed against it, has been incorporated into the American value system.

Calhoun asserts that Southern whites, outnumbered in the United States by voters of the more densely populated Northern states, are one such "minority" deserving special protection in the legislature.

Calhoun holds major political offices, serving terms in the United States House of Representatives, United States Senate and vice presidency, as well as secretary of war and state.

He usually affiliates with the Democrats, but flirts with the Whig Party and considers running for the presidency in 1824 and 1844.

As a "war hawk", he agitates in Congress for the War of 1812 to defend American honor against Britain.

As Secretary of War under President James Monroe, he reorganizes and modernizes the War Department, building powerful permanent bureaucracies that run the department, as opposed to patronage appointees.

Calhoun dies 11 years before the start of the American Civil War, but he is an inspiration to the secessionists of 1860–61.

Nicknamed the "cast-iron man" for his ideological rigidity as well as for his determination to defend the causes he believes in, Calhoun supports states' rights and nullification, under which states could declare null and void federal laws which they view unconstitutional.

He is an outspoken proponent of the institution of slavery, which he defends as a "positive good" rather than as a "necessary evil".

His rhetorical defense of slavery is partially responsible for escalating Southern threats of secession in the face of mounting abolitionist sentiment in the North.

Calhoun was one of the "Great Triumvirate" or the "Immortal Trio" of Congressional leaders, along with his Congressional colleagues Daniel Webster and Henry Clay.

In 1957, a Senate Committee selected Calhoun as one of the five greatest U.S.

Senators, along with Henry Clay, Daniel Webster, Robert La Follette, and Robert Taft.