On July 9, 1915, with the Central Powers pressing their advantage on the Western Front during World War I, the Allies score a distant victory, when military forces of the Union of South Africa accept a German surrender in the territory of Southwest Africa.

The Union of South Africa, a united self-governing dominion of the British empire, was officially established by an act of the British Parliament in 1910. When World War I broke out in Europe in the summer of 1914, South African Prime Minister Louis Botha immediately pledged full support for Britain. Botha and Minister of Defense Jan Smuts, both generals and former Boer commanders, were looking to extend the Union s borders further on the continent. Invading German Southwest Africa would not only aid the British—it would also help to accomplish that goal. The plan angered a portion of South Africa s ruling Afrikaner (or Boer) population, who were still resentful of their defeat, at the hands of the British, in the Boer War of 1899-1902 and were angered by their government s support of Britain against Germany, which had been pro-Boer in the Boer War.

Several major military leaders resigned over their opposition to the invasion of the German territory and open rebellion broke out in October 1914; it was quashed in December. The conquest of Southwest Africa, carried out by a South African Defense Force of nearly 50,000 men, was completed in only six months, culminating in the German surrender on July 9, 1915. Sixteen days later, South Africa annexed the territory.

At the Versailles peace conference in 1919, Smuts and Botha argued successfully for a formal Union mandate over Southwest Africa, one of the many commissions granted at the conference to member states of the new League of Nations allowing them to establish their own governments in former German territories. In the years to come, South Africa did not easily relinquish its hold on the territory, not even in the wake of the Second World War, when the United Nations took over the mandates in Africa and gave all other territories their independence. Only in 1990 did South Africa finally welcome a new, independent Namibia as its neighbor.