This was deemed illegal by Britain and the United Nations (UN), each of which imposed economic sanctions on Rhodesia. The two most prominent black nationalist parties in Rhodesia were the Zimbabwe African National Union (ZANU)—a predominantly Shona movement, influenced by Chinese Maoism—and the Zimbabwe African People's Union (ZAPU), which was Marxist–Leninist, and mostly Ndebele. ZANU and its military wing, the Zimbabwe African National Liberation Army (ZANLA), received considerable backing in training, materiel and finances from the People's Republic of China and its allies, while the Warsaw Pact and associated nations, prominently Cuba, gave similar support to ZAPU and its Zimbabwe People's Revolutionary Army (ZIPRA). ZAPU and ZIPRA were headed by Joshua Nkomo throughout their existence, while the Reverend Ndabaningi Sithole founded and initially led ZANU. The two rival nationalist movements began what they called their "Second Chimurenga" against the Rhodesian government and security forces, and, while based outside the country, sent groups of guerrillas into Rhodesia at regular intervals. Most of these early incursions, which had little success, were perpetrated by ZIPRA. Wilson and Smith held abortive talks aboard HMS Tiger in 1966 and HMS Fearless two years later. A constitution was agreed upon by the Rhodesian and British governments in November 1971, but when the British gauged Rhodesian public opinion in early 1972 they abandoned the deal on the grounds that they perceived most blacks to be against it. The Rhodesian Bush War suddenly re-erupted after two years of relative inactivity on 21 December 1972 when ZANLA attacked Altena Farm near Centenary in the country's north-east. The security forces mounted a strong counter-campaign and by the end of 1974 had reduced the number of guerrillas active within the country to under 300. In the period October–November 1974, the Rhodesians killed more nationalist fighters than in the previous two years combined. Mozambican independence and the South African "détente" initiative The effect of the security forces' decisive counter-campaign was undone by two drastic changes to the geopolitical situation in 1974 and 1975, each relating to one of the Rhodesian government's two main backers, Portugal and South Africa. In Lisbon, a military coup on 25 April 1974 replaced the right-wing Estado Novo administration with a leftist government opposed to the unpopular Colonial War in Angola, Mozambique and Portugal's other African territories. Following this coup, which became known as the Carnation Revolution, Portuguese leadership was hurriedly withdrawn from Lisbon's overseas territories, each of