In April 1975, the Frontline States – then consisting of Botswana, Tanzania and Zambia – were formally recognised as an entity as a committee of the Assembly of the Heads of State of the Organisation of African Unity. They were joined by Angola (1975), Mozambique (1975) and Zimbabwe (1980) when those countries gained their independence. Tanzanian President Julius Nyerere was the chairman until he retired in 1985.