Gresham's law
This resulted in a situation in which the greenback "Legal Tender" notes of 1862 were fiat, and so gold and silver were held and paper circulated at a discount because of Gresham's law. The 1861 Demand Notes were a huge success but robbed the customs house of much needed gold coin (interest on most bonds back then was paid in gold). A money-strapped Congress, which had to pay for the war, eventually adopted the Legal Tender Act of 1862, issuing United States Notes backed only by treasury securities, and compelled the people to accept the new notes at a discount; prices rose except for those who had gold and/or silver coins.