During his early presidency Kaunda was an outspoken supporter of the anti-apartheid movement and opposed white minority rule in Southern Rhodesia. Although his nationalisation of the copper mining industry in the late 1960s and the volatility of international copper prices contributed to increased economic problems, matters were aggravated by his logistical support for the black nationalist movements in Ian Smith's Rhodesia, South West Africa, Angola, and Mozambique. Kaunda's administration later attempted to serve the role of a mediator between the entrenched white minority and colonial governments and the various guerrilla movements which were aimed at overthrowing these respective administrations. Beginning in the early 1970s, he began permitting the most prominent guerrilla organisations, such as the Rhodesian ZANU and the African National Congress, to use Zambia as a base for their operations. Former ANC president Oliver Tambo even spent a significant proportion of his 30-year exile living and working in Zambia. Joshua Nkomo, leader of ZAPU, also erected military encampments there, as did SWAPO and its military wing, the People's Liberation Army of Namibia.