Starting in the early 1960s the three big liberation movements enjoyed support from a wide range of countries, in some cases even from the same. By the time of independence FNLA and UNITA received aid from the US, Zaire, South Africa, China and North Korea.
As long as Portugal was present in Angola, the movements had to have their headquarters in independent neighbouring countries, making Congo-Léopoldville (Zaire/Democratic Republic of the Congo, formerly Belgian), for both MPLA and FNLA a logical choice. After its expulsion from Léopoldville (now Kinshasa) in November 1963 the MPLA moved across the Congo River to formerly French Congo-Brazzaville (Republic of Congo), where it was invited by its new leftist government.
The FNLA stayed in Congo-Léopoldville to which it remained closely tied and from where it received the bulk of its support. FNLA leader Holden Roberto was linked to Mobutu by marriage and obligated to him for many past favours. Over the years the FNLA had become little more than an extension of Mobutu's own armed forces. Much of Zaire's support came indirectly from the US, which Zaire's leader Mobutu had close ties with. Zaire was the first country to send troops to Angola in March 1975 and to engage in fighting against the MPLA by the summer of that year.
In the summer of 1974 China was first to act after the Portuguese Revolution and posted 200 military instructors to Zaire where they trained FNLA troops and supplied military assistance. Chinese involvement was a measure against Soviet influence rather than that from western countries. On 27 October 1975, they were also the first to withdraw their military instructors. UNITA, which split away from FNLA in 1965/66 was initially Maoist and received some support from China. North Korea had been training Mobutu's elite division, the Kamanyola, also trained the FNLA but withdrew their support for Zaire and the FNLA by the end of December 1975. In 1975 China and North Korea were also the first to pull out of the area after the Portuguese Revolution. When their support ceased FNLA and UNITA became firmly established in the western camp.
The United States had a history of supporting the Salazar regime in Portugal, e. g. allowing NATO equipment to be used in Angola, as well as liberation movements fighting against Portuguese colonialism.
US support for the FNLA was taken up by the Kennedy administration in 1960. Holden Roberto had been on the CIA's payroll since 1963. On 7 July 1974, the CIA started funding the FNLA on a small scale. On 22 January 1975, one week after the Alvor Accords were signed and just before the provisional government of Angola was to take office, the US National Security Council's "40 Committee", which oversaw clandestine CIA operations, authorized US $300,000 in covert aid to the FNLA.
As the CIA was suspicious of the left-leaning MPLA it "had no wish to see the US government deal with the MPLA" and it did not want them to be part of the transitional government. The US increased its support for the FNLA and for the first time took up funding of UNITA. On 18 July 1975 US president Ford approved covert CIA operation "IAFEATURE" to aid FLNA and UNITA with money (US $30 million ), arms and instructors. US military instructors (CIA) arrived in southern Angola in early August where they closely cooperated with their South African counterparts who arrived around the same time. The support involved the recruitment of mercenaries and an expanded propaganda campaign against the MPLA. The American public was not informed. The US "was publicly committed to an embargo against the delivery of arms to Angolan factions while it was secretly launching a paramilitary programme". According to "the former chief of the CIA's Angola Task Force, John Stockwell, and from various other sources, it is now known that the US, far from seeking peaceful solutions, was instrumental in touching off the final round of fighting in 1975" that led to the Cuban intervention.
Other western countries with their own clandestine support for FNLA and UNITA were Great Britain and France. Israel aided the FNLA from 1963 to 1969 and the FNLA sent members to Israel for training. Through the 1970s Israel shipped arms to the FNLA via Zaire.
Some East bloc countries and Yugoslavia first established ties with the MPLA in the early 1960s during its struggle against the Portuguese. The Soviet Union started modest military aid in the late 1960s. This support remained clandestine, came in trickles and sometimes ceased altogether. This was the case in 1972, when the MPLA came under strong pressure from the Portuguese and was torn apart by internal strife (struggle between MPLA leader António Agostinho Neto and Chipenda from 1972 to 1974). Soviet aid was suspended in 1973 with the exception of a few limited shipments in 1974 to counter Chinese support for the FNLA; only Yugoslavia continued to send supplies to the MPLA. In response to US and Chinese support for the FNLA, Soviet support for the MPLA was resumed in March 1975 in the form of arms deliveries by air via Brazzaville and by sea via Dar-es-Salaam. Soviet assistance to the MPLA was always somewhat reluctant; they never fully trusted Neto and their relationship was to remain ambivalent through the following years.
The Soviets preferred a political solution, but they did not want to see the MPLA marginalized. Even after the South African incursions the Soviets only sent arms, but no instructors for the use of the sophisticated weapons. Among the other Eastern Bloc countries the MPLA had well established contacts with East Germany and Romania, the former shipping large amounts of non-military supplies.
Although being leftist, Neto was interested in an ideological balance in his foreign support, but in spite of "overtures" well into 1975, he was unable to procure support for the MPLA from the US, thus becoming solely dependent on the eastern camp.