In response to the 1966 ruling by the International Court of Justice, South-West Africa People's Organisation (SWAPO) military wing, People's Liberation Army of Namibia, a guerrilla group began their armed struggle for independence, but it was not until 1988 that South Africa agreed to end its occupation of Namibia, in accordance with a UN peace plan for the entire region. In what year did the UN start developing a peace plan for the whole region?