Economic sanctions are imposed by a government to show disapproval of another government's actions and to attempt to influence its future conduct. Economic sanctions involve the withdrawal or suspension of trade or financial relations.
The USA entered into a trade embargo with the USSR for the latter's invasion of Afghanistan, and several industrial countries have engaged in economic sanctions against South Africa in protest at the Platter's policies of apartheid. In 1989 India closed 13 of 15 entry points to the landlocked Kingdom of Nepal creating shortages of food, medicines and fuel.
The factors which really affected South African policy were not general trade sanctions. What really shook the government was that USA firms pulled out because it was not worth the aggravation of staying. Yet some sanctions were extremely effective. The sports boycott made white South Africans feel isolated in a way no economic sanctions could. The arms embargo also finally produced results when the South Africans were unable to match Angolan forces in 1988. Yet this military withdrawal led to a huge South African arms industry from which exports it now profits. Similarly the oil embargo created the oil-from-coal industry, although this is yet proving less of an good investment.