When the April 1974 revolution in Portugal brought about the downfall of the Portuguese African empire, the situation in Southern Africa was transformed.
In particular, new possibilities opened up for the liberation of Southern Rhodesia (Zimbabwe), either by negotiation if the white ruling minority could be induced to see reason, or by armed struggle if no other way was open.
Southern Rhodesia-racial discrimination and repression-report-1976-eng (full text in English, PDF)