Greenbacks first entered the scene during the Civil War. Up until that time, the federal government only minted coinage, not paper currency. But with the war on, the government needed to increase the money supply, and paper was the answer. The Bureau of Engraving and Printing used a new green ink, which was difficult to photograph, imitate, or erase, making it hard to counterfeit. In 1929, when the government switched to newer, smaller bills, it again chose green, but this time for different reasons: To begin with, it had a huge surplus of the pigment. More important, though, by this time, the color green had stuck -- it had, in fact, become a symbol of the might of the U.S. government.