16 December is a day of great significant in South Africa due to two historical events that took place. The first of these was in 1838, when the Battle of Blood River took place between the Voortrekkers and the Zulus. The Voortrekkers, having moved into the interior of South Africa during the Great Trek, were eager to settle on land. The region that they intended to settle on was already inhabited by the Zulu people. Thus the Voortrekker leader, Piet Retief was eager to negotiate with the Zulu chief Dingane. Having misunderstood Retief's intentions, Dingane planned an ambush and murdered Retief and his party of 100 people. This act culminated in the Battle of Blood River, in which 470 Voortrekkers, having the advantage of gunpowder, defeated the 10 000 strong Zulu army. This Voortrekker victory was commemorated since then as the Day of the Vow.
The second historical event that took place on 16 December was in 1961, when Umkhonto we Sizwe (MK) was formed. This was the military wing of the African National Congress (ANC), which was launched to wage an armed struggle against the apartheid government. Prior to its formation, the ANC had largely approached the fight against apartheid through passive resistance, but after the Sharpeville Massacre in 1960, where peaceful protestors were indiscriminately shot by police, passive resistance was no longer seen as an effective approach in bringing apartheid to an end. MK mostly performed acts of sabotage, but its effectiveness was hampered by organizational problems and the arrest of its leaders in 1963. Despite this, its formation was commemorated every year since 1961.
South Africa's first non-racial and democratic government was tasked with promoting reconciliation and national unity. One way in which it aimed to do this symbolically was to acknowledge the significance of the 16 December in both the Afrikaner and liberation struggle traditions and to rename this day as the Day of Reconciliation. On 16 December 1995, the Day of Reconciliation was celebrated as a public holiday in South Africa for the first time.
Read much more about the signifigance of 16 December here.
• Muller, C.F.J. (ed)(1981). Five Hundred years: a history of South Africa; 3rd rev. ed., Pretoria: Academica, p.166.
• Potgieter, D.J. et al. (eds)(1970). Standard Encyclopaedia of Southern Africa, Cape Town: NASOU, v. 2, p. 377.
• Reader's Digest. (1988). Illustrated History of South Africa: the real story, New York: Reader's Digest Association, pp.119 & 121.