On 24 October 1964, Zambia became independent of the United Kingdom and prime minister Kenneth Kaunda became the inaugural president. Kaunda's socialist United National Independence Party (UNIP) maintained power from 1964 until 1991. Kaunda played a key role in regional diplomacy, cooperating closely with the United States in search of solutions to conflicts in Southern Rhodesia (Zimbabwe), Angola, and Namibia. From 1972 to 1991 Zambia was a one-party state with UNIP as the sole legal political party under the motto "One Zambia, One Nation" coined by Kaunda. Kaunda was succeeded by Frederick Chiluba of the social-democratic Movement for Multi-Party Democracy in 1991, beginning a period of social-economic growth and government decentralisation. Zambia has since become a multi-party state and has experienced several peaceful transitions of power.