The agreement, signed by the People's Movement for the Liberation of Angola (MPLA), the National Liberation Front of Angola (FNLA), National Union for the Total Independence of Angola (UNITA), and the Portuguese government, was never signed by the Front for the Liberation of the Enclave of Cabinda (FLEC) or the Eastern Revolt as the other parties excluded them from negotiations. The coalition government established by the Alvor Agreement soon fell as the various nationalist factions, each distrustful of the other and unwilling to share power, attempted to take control of the country by force. The name of the agreement comes from the place where it was signed, the village of Alvor, located in the Portuguese southern region of Algarve.
Leftist military officers overthrew the Caetano government in Portugal in the Carnation Revolution on the 25th April 1974. The MPLA, FNLA, and UNITA each negotiated peace agreements with the transitional Portuguese government and began to fight each other for control of Luanda and the country. Holden Roberto, Agostinho Neto, and Jonas Savimbi met in Bukavu, Zaire in July and agreed to negotiate with the Portuguese as one political entity. They met again in Mombasa, Kenya on 5 January 1975, and agreed to stop fighting each other, further outlining constitutional negotiations with the Portuguese. They met for a third time in Alvor, Portugal from January 10–15 and signed what became known as the Alvor Agreement.
The parties agreed to hold the first assembly elections in October 1975. From the 31st January 1975 until independence, a transitional government consisting of the Portuguese High Commissioner Admiral Rosa Coutinho and a Prime Ministerial Council (PMC) would rule. The PMC consisted of three representatives, one from each Angolan party, and a rotating Premiership among the representatives. Every decision required two-thirds majority support. The twelve ministries were divided equally among the Angolan parties and the Portuguese government, three for each. Author Witney Wright Schneidman criticized this provision in Engaging Africa: Washington and the Fall of Portugal's Colonial Empire for ensuring a "virtual paralysis in executive authority". The Bureau of Intelligence and Research cautioned that an excessive desire to preserve the balance of power in the agreement hurt the transitional Angolan government's ability to function.
The Portuguese government's main goal in negotiations was preventing the mass emigration of white Angolans. Paradoxically, the agreement only allowed the MPLA, FNLA, and UNITA to nominate candidates to the first assembly elections, deliberately disenfranchising Bakongo, the Cabindese, and whites. The Portuguese reasoned that white Angolans would have to join the separatist movements and the separatists would have to moderate their platforms to expand their political bases.
The agreement called for the integration of the militant wings of the Angolan parties into a new military, the Angolan Defense Forces. The ADF would have 48,000 active personnel, made up of 24,000 Portuguese and 8,000 MPLA, FNLA, and UNITA fighters respectively. Each party maintained separate barracks and outposts. Every military decision required the unanimous consent of each party's headquarters and the joint military command. The Portuguese forces lacked equipment and commitment to the cause while Angolan nationalists were antagonistic of each other and lacked training.
The treaty, which FLEC never agreed to, described Cabinda as an "integral and inalienable part of Angola". Separatists see the agreement as a violation of Cabindan right to self-determination. By August 1975 the MPLA had taken control over Cabinda.
The agreement did not establish a mechanism to verify the number of fighters from each force, an error criticized by author Donald Rothschild. All three parties soon had forces greater in number than the Portuguese, endangering the colonial power's ability to keep the peace. Factional fighting renewed, reaching new heights as foreign supplies of arms increased. In February the Cuban government warned the Eastern Bloc the Alvor Agreement would not succeed. By spring the African National Congress and SWAPO were echoing Cuba's warning. Leaders of the Organization of African Unity organized a peace conference moderated by Kenyan President Jomo Kenyatta with the three leaders in Nakuru, Kenya in June. The Angolan leaders issued the Nakuru Declaration on 21 June, agreeing to abide by the provisions of the Alvor Agreement while acknowledging a mutual lack of trust led to violence. Many analysts have criticized the transitional government in Portugal for the violence that followed the Alvor Agreement in terms of a lack of concern about internal Angolan security and favoritism towards the MPLA. High Commissioner Coutinho, one of the seven leaders of the National Salvation Junta, openly distributed ex-Portuguese arms and military equipment to MPLA forces at the expense of the other competing parties.
Edward Mulcahy, Acting Assistant Secretary of State for African Affairs in the United States State Department, told Tom Killoran, the U.S. Consul General in Angola, to congratulate the PMC rather than the FNLA and UNITA on their own and Coutinho for Portugal's "untiring and protracted efforts" at a peace agreement. Secretary of State Henry Kissinger considered any government involving the pro-Soviet, Communist MPLA, to be unacceptable and President Gerald Ford oversaw heightened aid to the FNLA.
In July the MPLA violently forced the FNLA out of Luanda and UNITA voluntarily withdrew to its stronghold in the south. There MPLA forces engaged UNITA and UNITA declared war. By August the MPLA had control of 11 of the 15 provincial capitals, including Cabina and Luanda. South Africa intervened on 23 October, sending 1,500 to 2,000 troops from Namibia into southern Angola. FNLA-UNITA-South African forces took five provincial capitals, including Novo Redondo and Benguela in three weeks. On 10 November the Portuguese left Angola. Cuban-MPLA forces defeated South African-FNLA forces, maintaining control over Luanda. On 11 November Neto declared the independence of the People's Republic of Angola. The FNLA and UNITA responded by proclaiming their own government based in Huambo. By mid-November the Huambo government had control over southern Angola and began pushing north.