As it says in the title: in 1804 the British gave the Cape Colony back to the Dutch, after the Dutch had begged Britain to take it over in the 1790s (at least that's the history I was taught at school). Then in 1804, IIRC (it was half a lifetime ago that I was taught this, so forgive me if I'm a bit rusty), the British bought from the Dutch or the Dutch sold the Cape to the British. There was something about how the motivation behind this (on the Dutch side) was that the prince of Orange had pressing debts and he needed the money.
As a result, the colony had to deal with the inundation of British ("souties" if they weren't soldiers, "rooinekke" if they were soldiers), and in the 1830s,a bunch of like-minded Afrikaners (Dutch/French hugenot descended settlers) decided to Hell with the King and Westminster, and went on the Groot Trek.
Now, if the Dutch hold onto it, obviously the British are going to take it back again when war breaks out with France, so as to prevent France from getting it, but say at alt-Vienna it's decided to give it back to the newly-enlarged kingdom of the Netherlands. What might the future hold for South Africa if it stays in the hands of the Dutch rather than being sold to the British? What effect, if any, will it have on the Dutch situation in Europe?