The Nullification Crisis was the first real secession crisis in U.S. history. It was caused by a tariff, or import duty, on foreign goods. The idea was to spur American manufacturing, and with that in mind the tariff was passed by congress in 1828.
Although northern manufacturers loved how it encouraged people to buy more American made products, it did result in a slow down of trade with other nations. This angered southerners, who relied on cotton exports for their livelyhood.
It was so unpopular that southern political theorists came up with a way around it. Nullification was a doctrine that said states had the right to decide whether or not to obey each law passed at the federal level. The states more or less decided what laws were "null and void"
Although this idea was originally thought up by others more than 20 years earlier, it was South Carolina that came up with an added part. If a state doesn't like what the government is doing, it can secede, or leave, the Union. This would eventually lead to the Civil War 30 years later, but when Andrew Jackson threatened total war if South Carolina tried to secede, they backed off. The taiff was later reduced and peace was restored.
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