In the history of southern Africa 31 May is a date that recurs many times, and it isn't a coincidence.
On 31 May 1902 the Boers surrendered to international capitalism which, through British military force, had defeated them, wiping out about the 50% of the Boer child population.
On May 31, 1902, the Boers signed the Treaty of Vereeniging, which ended the Boer Republics and deprive them of freedom.
The south African Empire, established in 1902 with the conquest of the Boer Republics, began to promotes a new false “nationalism” primarily based on skin color (not even on the race!), for to contrast the true Boer nationalism, which demanded the lost freedom. This new “nationalism” was aimed to tie together the white peoples of the Empire: the Cape Dutch (then know as Cape [white] “Afrikaner”); the Boer; the British.
To promote this false “nationalism”, finalized principally to delete the Boer identity and put down the desire for freedom of that volk, they tried to involved the Boers on the Empire that had conquered them. The Boers were not to see that Empire as an enemy, otherwise they would fight against it, but as something of their own. That was the plan for southern Africa, conceived by international capitalism and summarized by the prime representative of the British Empire in southern Africa, Sir Alfred Milner: “The new tactic (to subjugate the Boers) must be to consolidate the different areas of British South Africa into one nation. Although unification will be initially put the Boers into political control of the entire South Africa, it will, ironically, eventually lead to their final downfall.”
Under this plan, the date of May 31, 1902, was not to be remembered by the Boers as the end of their freedom, but as a simple stage of their national history, which continued into a new state (an empire!). For this the date of May 31 was used by the Empire of southern Africa on several occasions, to give the Boers the idea of a new beginning, a new 31 May that re-established the freedom lost on May 31, 1902. But they were just illusions. The Empire that had conquered the Boer republics was not a Boer state, but its worst enemy.
On May 31, 1910, was established the Union of South Africa, which included the former British colonies and the former Boer republics conquered (then: an empire).
On 31 May, 1928, the Union of South Africa (Empire) adopted the “Oranje-blanje-blou” flag (a collage of different flags) to replace the British flag.
On 31 May, 1961, the empire of the Union of South Africa transform itself in the Republic of South Africa (RSA).
31 May was “Union day” for the Union of South Africa, from 1910 to 1960, and “Republic day” for the Republic of South Africa, from 1961 to 1993.
But the Boers don't celebrate 31 May. On 31 May the Boers remember their lost freedom, in 1902. The same freedom that must be restored.