In December 1988, a US-mediated peace agreement linked the UN Resolution 435 was signed by South Africa, Cuba, and Angola, setting a timetable for Namibian independence; at the same time Cuba and Angola agreed to a phased withdrawal of Cuban troops from Angola. However, during Namibia's transition period, SWAPO [South-West Africa People's Organisation] forces based in southern Angola swarmed into Namibia on April 1, 1989, in violation of the peace agreement. Waiting for the guerrillas were Namibian security police, who killed several hundred of them and stopped the SWAPO incursions. Afterward, thousands of Namibian refugees and exiled SWAPO members, including Samuel S. Nujoma (1929-), longtime political leader, returned peacefully to Namibia. A Constituent Assembly was then elected to frame a constitution; Nujoma took office as president when South Africa relinquished its control and gave Namibia full independence on March 21, 1990.