Alfheim & Svartalfheim Elves

The worlds of Alfheim & Svartalfheim are the original worlds of the Elves. The former translates as Elf Home, and the latter translates as Black Elf Home. Both are part of the nine worlds of Yggdrasil in Norse belief. In both cases they view the elves in the Feywild, the Seelie Court, the Unseelie Court, and the Shadar-Kai in Shadowfell as upstarts. The elves originally evolved on the world of Alfheim, and worship the Aesir & Vanir(the gods on the worlds of Asgard & Vaniheim). They were two distinct groups. The high elves who practised magic, war, the arts, and architecture. They have standing armies, impressive beautiful cities and a rich culture. The wood elves are more rustic and closely tied to nature, living in communities in forests, and tied to agriculture, animal husbandry, and nature magic. Given time both groups started to grow complacent, and some started to show signs of breaking away from either of these two traditions. Both traditions have deep respect for each other to this day, but these elves that started to show entirely different mindsets. Grouping together, they became more & more domineering and aggressive, as well as starting to worship other deities. This led to a schism that caused a war that they could not win, given their numbers. Before this time, they had begun to live underground, believing their new deities lived there, and their physiology started to change too, becoming more and more used to darkness. Eventually they were assailed and driven out of Alfheim, and forced to travel to to what became Svartalfheim.
Svartalfheim is a rocky world with riches deep underground, and these new elves soon adapted to their new world with ease. Their ability to see in darkness improved at the expense of their tolerance to sunlight. Their hair & skin pigmentation changed due to lack of sunlight & the compounds in their new environment. Now pale, purple, blue, and in the majority, black pigmentation of hair, eyes, and or skin is common, amongst these elves. They took a new name calling themselves Black Elves, Dark Elves, or Drow. The black elves are primarily atheistic, or at the very least paying lip service to gods, while the black elves worship one of two gods called Khaine or She Who Thirsts. As for the Drow, they worship the goddess of spiders, a being they call Lolth. They thought they were the only beings on Svartalfheim, but were greatly mistaken. Growing in numbers deeper still, was the ancestors of the Dwarves. Expert craftspeople, the dwarves to this day still make some of the best weapons and armour available. With their strong tough minds & bodies, as well as equipment they fought the black kin of the elves, dominating massive swathes of Svartalfheim.
With these wars, and the growth of the populations of high elves & wood elves, many migrated to other worlds. The first world they encountered was Midgard on the Material Plane and proceeded to take up residence in regions there. These are in present day Germanic regions, and they found these tribes speak languages loosely related to other worlds on Yggdrasil. In many instances the black elves were driven underground where they still are, while the high & wood elves are accepted by the early Germanic peoples, and even the dwarves (though begrudgingly) who could see that the latter two are nothing like their evil siblings.
From there they have spread into Celtic lands and regions that would eventually become Slavic land where they are still present, and would interact the locals. In these lands the locals would eventually build up their own traditions & beliefs about the elves, and they would form beliefs themselves that deviated from their ancestors. Because of this they also came across the Fey, and were able to mingle freely with them, changing in a fundamental way, spiritually, and to a lesser degree physically due to the effects of Fey magic and the Feywild that permeates anything touched by it.