There. I think that covers them all. Can anyone tell if I missed anything?
Don't mind if I do
It basically comes to this: at the dawn of the mortal world, we had the Hists and the Ehlnofey (Argonians are mutant Hist or something). The Ehlnofey wandered around for a bit before settling down, then began to differentiate racially. Those who settled in the northern continent of Atmora evolved into humans called Nedes. The Ehlnofey that settled in the western continent of Yoduka became humans called Redguards. Those who settled in Tamriel became elves called Aldmer. Eventually, the Aldmer began to form their own nations and races: the Falmer (snow elves), Altmer (High Elves), Ayleids (Heartland High Elves), Maomer (mayonaiseTropic Elves), Dwemer (Dwarves), and probably others we haven't heard of yet.
Wrong. Or rather, not enough "right"
There were elves in Yokuda and Atmora, as well as there were men in Tamriel. The man/mer split of the Ehlnofey is the result of the fraction amongst the et'Ada - whether they sided with Lorkhan or "the Aedra". It's not a matter of "where" they finally settled down.
Anyway - both the elves of Yokuda and the elves of Atmora were defeated and eradicated by their human antagonists - either this happened after the "settling down" part of Ehlnofey history, or it happened during the war between Lorkhan and "the Aedra" (seriously, is there a better word for that group of et'Ada? I can't remember, and it bugs me to hell - it definitly feels like I'm using the wrong term). In the later case, the stories would be myth echos of the original event. Or, perhaps it is both.
Eventually, Atmora began to freeze over due to climate change. So, the Nedes slowly began migrating to Skyrim in northern Tamriel, driving out the native Falmer. In time, some of them interbred with elves, creating the part-human part-elven Bretons. The Nedes then eventually started to be called Nords.
As been said, there were already humans in Tamriel - Bretons (or their precursors, the "manmer") are the result of the intermingling of those and the Elves of the region.
Some elves in Valenwood interbred with humans. This produced the Bosmer (Wood Elves.)
Not exactly. How would mixing with humans give the Bosmer horns, or bug eyes? Rather, their "mannish" wives could have been the "forest people" (or whatever they were at the time) of the region. The "forest people" did not know their shape, after all, and would explain the "monsterous" parts of the Bosmer, and also their shapeshifting ability/curse.
At one point, the goddess Azura took some Bosmer, led them east to Elsweyr, and transformed them into the Khajiit. According to the Khajiit, this was so that they could help stop the apocolypse or something like that.
Nay. Azura took some of the "forest people" (again, those who "did not know their shape") and made them into Khajiit. They are not related to elves any more than humans are. According to the Khajiit "creation myth", Y'ffre created the Bosmer out of the "forest people" as well - this is most likely just paraphrasing of the story about how he became an Earthbone and alloved the pre-elves to take (stay in) their elven shape.
Meanwhile, the High Elves of Summerset Isle became decadent and spoiled. A few conservative religious wacks among them left for the eastern region of Morrowind, calling themselves the Chimer. There, they ended up fighting a war with the native Dwemer. The Dwemer attempted to harness the power of the heart of the dead god Lorkhan to defeat the Chimer. This did not work, and they vanished from the mortal world in the process. Four of the Chimer attempted to use the Heart of Lorkhan themselves, and succeeded in becoming demigods. However, Azura appeared and punished them for attempting to make themselves gods. She cursed the entire Chimer people, making them ugly and stunting their magic abilities. They became the Dunmer (Dark Elves.)
Not conservative - the Chimer/Velothi were/are definitely "reformists". The rest about the Dwemer/Chimer is very simplyfied, but I can agree that that was basically what happened
how did the akavier races come about
Adding to what Lady Nerevar said, it should be noted that the Tsaesci (woo! I could spell that correctly without checking TIL first for the first time! :foodndrink: ) are (were) the "men" of Akavir, and the Ka'Po'Tun are the "elves". Mythopoeically speaking, that is.
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Did I use "mythopoeic" right, by the way? Aside from the horrible grammar bending, that is. Maybe it should be "mythopoetically". The grammar Wiki likes both of them.