The diminishing number of elephants, to a large extent the result of wholesale slaughter for tusks, and the resulting increased cost of ivory have encouraged the making of imitations and the use of natural substitutes. One strategy for controlling the slaughter of elephants for their ivory is to permit a regulated trade that would reduce poaching and provide profit to Africans, but not deplete the elephant population. A ban of the ivory trade, with some limited exceptions, by countries that supply and consume ivory has been in effect since 1989. Despite this ban, the ivory trade has continued illegally in a number of producing and consuming countries, with increasingly devastating effects on elephant populations in the 21st cent. The illegal trade also has contributed to political instability, with rebel groups using it to fund their operations.