"King Cotton" is a slogan that summarized the strategy used before the American Civil War (of 1861–1865) by pro-secessionists in the southern states (the future Confederate States of America) to claim the feasibility of secession and to prove there was no need to fear a war with the northern states. The theory held that control over cotton exports would make a proposed independent Confederacy economically prosperous, would ruin the textile industry of New England, and—most importantly—would force the United Kingdom and perhaps France to support the Confederacy militarily because their industrial economies depended on Southern cotton. The slogan, widely believed throughout the South, helped in mobilizing support for secession: by February 1861, the seven states whose economies were based on cotton plantations had all seceded and formed the Confederacy. Meanwhile, the other eight slave states, with little or no cotton production, remained in the Union. To demonstrate the alleged power of King Cotton, Southern cotton merchants spontaneously refused to ship out their cotton in early 1861; it was not a government decision. By summer 1861, the Union Navy blockaded every major Confederate port and shut down over 95% of exports. Since the British mills had large stockpiles of cotton, they suffered no immediate injury from the embargo; indeed the value of their stockpiles soared. For Britain to have intervened would have meant war with the U.S. and a cut-off of food supplies. About one-fourth of Britain's food supplies came from the United States, and American warships could destroy much of British commerce while the Royal Navy was convoying ships full of cotton. The British did not react to King Cotton, and they never intervened. Consequently, it proved a failure for the Confederacy, as the strategy did not succeed in making the new Confederate polity economically prosperous. The blockade prevented the earning of desperately needed gold. Most importantly, the false belief led to unrealistic assumptions that the war would be won through European intervention if only the Confederacy held out long enough.