Since 1870, there have been several formal attempts to restrict the copper output and raise, in this form, its price. This is a list of copper cartels in the 20th century: * Copper Export Association, CEA, 1918–1923 * Copper Exporters, Inc., CEI, 1926–1932 * International Copper Cartel, ICC, 1935–1939 (Also called World Copper Agreement) * Intergovernmental Council of Copper Exporting Countries, CIPEC, 1967–1988