But, of his dark and dangerous sort, Calhoun was an able man. He foresaw early that the best weapon of the common interest of the slave States lay in the rights which might be claimed for each individual State against the Union. The idea that a discontented State might secede from the Union was not novel--it had been mooted in New England, during the last war against Great Britain, and, curiously enough, among the rump of the old Federalist party, but it was generally discounted. Calhoun first brought it into prominence, veiled in an elaborate form which some previous South Carolinian had devised. The occasion had nothing to do with slavery. It concerned Free Trade, a very respectable issue, but so clearly a minor issue that to break up a great country upon it would have gone beyond the limit of solemn frivolity, and Calhoun must be taken to have been forging an implement with which his own section of the States could claim and extort concessions from the Union. A protective tariff had been passed in 1828. The Southern States, which would have to pay the protective duties but did not profit by them, disliked it. Calhoun and others took the intelligible but too refined point, that the powers of Congress under the Constitution authorised a tariff for revenue but not a tariff for a protective purpose. Every State, Calhoun declared, must have the Constitutional right to protect itself against an Act of Congress which it deemed unconstitutional. Let such a State, in special Convention, "nullify" the Act of Congress. Let Congress then, unless it compromised the matter, submit its Act to the people in the form of an Amendment to the Constitution. It would then require a three-fourths majority of all the States to pass the obnoxious Act. Last but not least, if the Act was passed, the protesting State had, Calhoun claimed, the right to secede from the Union.