The study done in 1969 can be found at this link, https://history.state.gov/historicaldocuments/frus1969-76v28/d17 - “Study in Response to National Security Study Memorandum 39: Southern Africa”. It is interesting to read their “options” to deal with South Africa, Rhodesia and the Portuguese territories. Below are a few exerpts.
“The racial problems of southern Africa probably will grow more acute over time, perhaps leading to violent internal upheavals and greater involvement of the communist powers. Though these developments may be years or even decades ahead, U.S. policy should take account now of the risks to our interests and possible involvement over this uncertain future.”
“The results will be: (a) black guerrilla and terrorist activity on a growing scale within these countries until change occurs, and (b) because of their support of the blacks, the Soviets and Chinese will become the major beneficiaries of the conflict.”
“Others contend that there will be violence up to a point, since change can only come slowly. But there is some prospect for peaceful change in the white states in response to internal economic and social forces.”
“Only isolation and stronger forms of pressure (i.e. force or mandatory economic sanctions backed by blockade) could have any impact.”
“Others argue that our tactical encouragement of economic and social forces already at work within the white regimes can constitute marginal but important influence for change. That influence, however, can be exerted only subtly and over several years.”
“Some argue that racial hostility as a reaction to centuries of white predominance is a relatively new political force in the world, gaining power and effectiveness as the developing countries become independent and control access to their own territories. We cannot foresee exactly when race will become a major factor in the international power balance, but that time is coming.”
“This policy seeks progress towards majority rule through political arrangements which guarantee increasing participation by the whole population.”
“The mandatory sanctions program [Southern Rhodesia] was devised by the British as a compromise between the use of force, which they were unwilling to contemplate largely because of domestic considerations, and doing nothing, which would have jeopardized their relations with the black African states and other Afro-Asian members of the Commonwealth. The United States cooperated with the U.K. largely for the same reasons.”
“Investment guarantees are available, and the U.S. extends additional help through PL 480 food donations, and Peace Corps programs in four of the five black countries.”
“The U.S. maintains contact with exile nationalist movements from the white-controlled states. We also assist refugee students from these states through the Southern African Student Program and two secondary schools which are operated for refugee students.”