Nords came from Atmora, Atmora did exist.
Mostly true. It's more complicated than that thought.
Its the RETURN because he came back after the night of tears with his companions too kick Falmer ass.
Actually, that's completely untrue. The ingame books, chiefly the Anuad, the Songs of the Return, Yngol and the Sea Ghosts, and the various books about the dragon cult all paint a pretty clear picture of Nordic history. To review, lets go all the way to the Dawn Era and the Ehlnofey. Of the progenitor Ehlnofey, there were two groups, the Old (or the ancestors of the Mer, living the high life on what would later be known as Aldmeris) and the Wandering Ehlnofey, who would later become the races of Men. The myths speak of the Wandering Ehlnofey being overjoyed to find their kindred still living in Aldmeris. Unfortunately, the Old Ehlnofey considered the wanderers corrupt, and told them to get the hell out. The wanderers then dispersed over various areas, becoming the Redguards of Yokuda, the Atmorans or proto-Nords (remember, the Nordic national identity didn't start to coalesce until around king Haralds time, about 13 generations after Ysgramor), the Cyrodiilic native groups, and the Tsaesci of Akavir. The relevent elven legends that this time speak of "Aldmora" or the "Ancient Wood" being " lost" to the Wandering Ehlnofey, or men. At this point, Aldmora of the Elves becomes Atmora of Men.
Despite this, The Atmorans/Proto-Nords
always maintained that the Throat of the World was the Genesis point of their Creation. This is attested to by several ingame books. One of them specifically mentions this fact as being why Ysgramor's original pre-Night of Tears Journey was thought of as a "Return" as well. Since the Atmorans believed the ToTW was their creation point, they had ancestral claim to the land. I can't remember the exact text that appeared in, but I'll look it up when I get home.
Fastforward to the Merethic Era. Atmora is wracked by civil war, which is probably also compounded by dramatic climate shifts, which Ysgramor was fleeing on his first journey. After Saarthal was sacked and Ysgramor returned to Atmora, he found the civil war ended and a realm of peace, but apparently the climate shifts were still well underway. Instead of staying in Atmora, Ysgramor made his second journey (which technically, would be be the "return of the return") with his 500 companions (minus one son and his ship and crew before they even hit shore). After they *mostly* cleared Skyrim out of the Mer, large scale immigration from Atmora to Skyrim began, which probably was still continuing until the Second Era. We know that the official Imperial biography of Tiber Septim is BS, but his scribes wouldn't have included that he was an immigrant from Atmora unless it was still a feasible proposition. We also know that the climate changes in Atmora would eventually have rendered it mostly uninhabitable. After all, in the ingame histories, Ysgramor orders his tomb placed on the shore, facing Atmora so that he may contemplate it's beauties "before the freezing took it". I suspect now that most of Atmora is a frozen, depopulated wasteland.
In short:
1) Nords believe they were created in Skyrim
2) for a variety of reasons, they relocated to Atmora. They probably displaced a pre-existing elven civilization there. An interesting theory is that the Snow Elves were the original inhabitants of Aldmora/Atmora ,being displaced to Skyrim by the early Atmoran humans, and then being displaced/eradicated again after humans returned to Skyrim.
3) After civil war breaks out in Atmora and the weather goes to crap, a process of migration from Atmora back to Skyrim again
4) The immigrant Atmorans form a new national identity as Nords.
EDIT:
From the Imperial Geographic Society:
For hundreds of years in the Merethic Era, raiders crossed the Sea of Ghosts to invade Tamriel from the frozen lands of Atmora, becoming after generations of living in our land the Nords, Cyrodiils, and the Bretons of today. The last invasion - if that is the word for two ships, largely laden with corpses, begging to make port - occurred in the 68th year of the First Era. The description of the land these raiders had left changes radically over the years, leaving many to believe that it was gradually dying, smothered by frost. Expeditions to Atmora in modern times describe a place of permanent winter, with little life and no sign of human habitation. Whatever population did not succeed in fleeing to Tamriel doubtless succumbed to the ever-worsening climate many centuries ago.
Even before the frost fall, Atmora was apparently not a temperate place. The early Nedic peoples who came from Atmora were hunters with no knowledge of agriculture. A land where every denizen was a predator doubtless insured that only the most brutal and savage survived. It is easy to see how these traits passed the raider men and down to the nature of the Arena of Tamriel.
I'm still sticking to my asserition that the immigration continued into the SE, however. The Geographic society has been proven to have a spotty record.