4 April 1989
The South African government threatened to pull out of the United Nations (UN) peace plan for Namibia unless action was taken against the South West African People's Organisation (SWAPO)  fighting near the northern border. In 1988, under a UN brokered peace initiative, the South African government agreed to give up control of Namibia. The story of South Africa occupying German South West Africa (now Namibia) started in May 1915 when General Louis Botha, first Prime Minister of the Union of South Africa, ordered 40 000 South African troops into the territory. Heavily outnumbered, the German forces were forced to retreat. The colony surrendered on 9 July 1915, bringing 31 years of German rule to an end. On 21 March 1990, Namibia was granted its independence by South Africa.
References

South African History Online, ‘Namibia gains Independence’,From: South African History Online [online], available at www.sahistory.org.za [Accessed on 14 March 2013]|Boddy-Evans, A. ‘This Day in African History: 4 April’, from About African History, [online], available at africanhistory.about.com (Accessed: 14 March 2013)|South African History Online‘Namibia’,From: South African History Online, [online], available at www.sahistory.org.za