The three liberation movements proved unable to constitute a united front after the Portuguese coup in 1974. By 1975, the FNLA's internal support had dwindled to a few Bakongo groups, but it had strong links with the Zairean regime and was well armed; it thus made a bid to seize Luanda by force. The MPLA, with growing backing from the Portuguese Communist Party, Cuba, and the Soviet Union, defeated this onslaught and then turned on UNITA, chasing its representatives out of Luanda. UNITA was militarily the weakest movement. At the time, it claimed the allegiance of about 40 percent of the population.
When the Popular Movement for the Liberation of Angola (MPLA) gained control of Angola's central government in 1976, the National Union for the Total Independence of Angola (UNITA) and the National Front for the Liberation of Angola (FNLA), two separate factions fighting for ascendancy, refused to recognize the new marxist-oriented government. In 1977, the MPLA captured the last major stronghold of the UNITA, whose leaders then fled to neighboring Zaire and Zambia, where they regrouped and revived their guerrilla warfare against the MPLA. White mercenaries, South Africans, and Portuguese frequently aided UNITA militarily, and covert American arms and assistance were reportedly received as well. In 1977, UNITA initiated a series of guerrilla raids on urban areas in Angola; a rebellion that UNITA supported was crushed. The following year a government offensive against the guerrillas failed to dislodge them from the large areas they controlled in southern Angola. Being sympathetic to South Africa, UNITA let South African forces maintain bases in its territory for raids into Namibia, or South West Africa. In the early 1980s, UNITA guerrillas had extended their control to central and southeast Angola. They won the support of Great Britain, France, the United States, Saudi Arabia, and a number of African nations, while the MPLA was backed by the Soviet Union and Cuba. The continual warfare disrupted Angola's economy and displaced one-sixth of its people, many of whom were forced to become refugees in Zaire, Zambia, and the Congo. The United States refused to recognize Angola's government as long as Cuban troops were in the country. In late 1988 US-mediated talks led to a signed peace accord, after which South Africa removed its troops, but the fighting continued between the marxist MPLA government and the UNITA rebels. Another truce in June 1989, signed by Angola's President Jose Eduardo dos Santos (1942-) and UNITA leader Jonas Savimibi (1934-2002), also failed to end hostilities. Cuba removed its troops in May 1991. After a year of negotiations, led by the Soviet Union and the US, Santos and Savimbi signed a peace treaty in Lisbon, Portugal, on May 31, 1991, officially ending the 16-year civil war.