In reaction to the prediction by Thomas Malthus that the world's population would soon outgrow its food supply, a movement began in the early twentieth century to limit the number of births and therefore limit the growth of the world's population. The movement is supported by groups such as the International Planned Parenthood Federation. A number of countries have made population control a national policy. To varying extents, the methods of population control include family planning, birth control, contraception, and abortion. These policies are opposed by many groups, including the Roman Catholic Church, and are controversial.