"FAPLA had substantially improved its capabilities and performance. In the first place, FAPLA had begun to develop and acquire the organization, doctrine, and equipment of a conventional army only during the civil war of 1975—76. It was then forced to fight a counterinsurgency war in the most remote and inaccessible parts of the country over extended lines of communications, without the requisite air
or ground transport or logistical infrastructure. Only after sufficient aircraft and air defense systems had been deployed in the mid-1980s Luanda was able to launch and sustain large offensives in the south. Although they suffered heavy losses and perhaps relied too heavily on Soviet military doctrine, FAPLA and FAPA/DAA in the late 1980s showed increased strength, put greater pressure on UNITA, and raised the costs of South Africa's support for UNITA. Luanda's resolve and the improved capabilities and performance of its armed forces were among the essential conditions under which South Africa agreed to negotiate its withdrawal from Angola."
"Angola: a country study". Edited by Thomas Collelo, published in 1989 by the Federal Research Division of the US Library of Congress