After the security forces mounted a successful counter @-@ insurgency campaign during 1973 and 1974 , developments overseas caused the conflict 's momentum to shift in the insurgents ' favour . The leftist Carnation Revolution of April 1974 caused Portugal to withdraw its key economic support for Smith 's administration , and led to Mozambique 's independence the following year as a communist state openly allied with ZANU . Around the same time , Rhodesia 's other main backer , South Africa , adopted a détente initiative that forced a ceasefire , giving the guerrillas time to regroup . Following the abortive Victoria Falls Conference of August 1975 , Smith and the ZAPU leader Joshua Nkomo held unsuccessful talks between December 1975 and March 1976 . ZANU and ZAPU announced in October 1976 , during the run @-@ up to the unsuccessful Geneva Conference in December , that they would henceforth attend conferences as a joint " Patriotic Front " .