The 16th of December is a day of great significance in South Africa because of two historical events that took place on that date.
In apartheid South Africa 16 December was known as Day of the Vow, as the Voortrekkers in preparation for the Battle of Blood River on 16 December 1838 against the Zulus took a Vow before God that they would build a church and that they and their descendants would observe the day as a day of thanksgiving should they be granted victory.
The second historical event that took place on 16 December was in 1961, when Umkhonto we Sizwe (MK), the military wing of the African National Congress (ANC), was formed. 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. With the advent of democracy in South Africa 16 December retained its status as a public holiday. 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.