Two of the greatest mysteries in The Elder Scrolls involve the unknown fates of the Dwemer and the Akaviri, two races that have seemingly disappeared. The fantasy RPG series has an exceptional amount of lore related to its universe's history, with the games taking place thousands of years into the era of recorded history. Many societies, cultures, and empires have risen and fallen in The Elder Scrolls, but the ultimate fates of the Dwemer and the Akaviri are unknown.
The Dwemer are (or were) a race of Elves which inhabited Tamriel, the continent on which The Elder Scrolls takes place. The in-game universe's mortal plane, Mundus, houses the planet Nirn, which consists of more than just Tamriel, even though other continents and land masses have never been seen by players. This includes Akavir, a continent to the Tamriel's west across the Padomaic Ocean. Though there are many inhabitants of Akavir, mentions of the Akaviri usually refer to a race of Men which have only been seen a handful of times throughout Tamrielic history.
As far as impact on The Elder Scrolls games themselves, the remnants of the Dwemer are far more present, having built some of the deepest dungeons in Skyrim in the form of vast, underground complexes. The Akaviri are a bit more nebulous, never establishing significant settlements or cities in Tamriel. Both, however, have mysteriously disappeared by the Third Era, when the first four Elder Scrolls games take place, and there is very little evidence pointing toward what actually happened.
The Unknown Fate Of Skyrim's Dwemer
The disappearance of the Dwemer is a matter of ancient history, occurring over three and a half millennia before The Elder Scrolls: Arena. Sometime before the recorded history of the First Era began, in what is known as the Merethic Era - when Elves (or Mer) dominated Tamriel - the Dwemer primarily settled in the regions that would one day become the provinces of Morrowind and Skyrim. By the early centuries of the First Era, the Dwemer had already constructed many of their signature underground complexes, including Skyrim's massive and secretive Blackreach. Within their subterranean cities, the Dwemer made great and revolutionary advancements in many fields, including technology, metallurgy, construction and infrastructure, science and mathematics, and magic.
Like most civilizations in The Elder Scrolls, the Dwemer were far from peaceful, and their history is riddled with not only wars against competing nations, but also civil war. Most notably, perhaps, the Dwemer, along with another race of Elves known as the Chimer, were responsible for expelling the Nords from Morrowind in the First Era, forcing them back to their ancestral home in Skyrim. Their most notorious exploit, though, was the enslavement of the Falmer, who were seeking refuge from the Atmorans during the War of the Crag. After fleeing into the Dwemer's underground cities, their enslavement directly contributed to their devolution into the Falmer monster players fight in Skyrim, a process aided by a toxic fungus they were forced to ingest, though not the same plant found in Blackreach by Oblivion and Skyrim's obsessive Nirnroot quest-giver.
Dwemer civilization would not last past the first millennia of the First Era, though, with the Battle of Red Mountain in 1E 700 resulting in their mysterious disappearance. Deep inside the Red Mountain, the Dwemer believed they had found an ancient artifact called the Heart of Lorkhan, which was central to Chimer cultural beliefs. The god Lorkhan, according to legend, tricked the Aedra into creating Mundus, and had his heart ripped out and hidden in Nirn as punishment. The Chimer believed the supposed discovery of the Heart of Lorkhan was the Dwemer making a mockery of Chimer beliefs, and the Battle of Red Mountain commenced. During the battle, the Dwemer attempted to use the Heart in order to ascend the Dwemer into divinity. Though it is unconfirmed, the experiment is believed to have resulted in a temporal anomaly that essentially erased the Dwemer from material existence instead.
The Unknown Fate Of The Akaviri
While the exact fate of Skyrim's Dwemer is unknown, it's generally believed that they were unceremoniously removed from the mortal plane, but that of the Akaviri is even more nebulous. The main issue with discerning the fate of the Akaviri is the general mysteriousness surrounding the continent of Akavir itself. Very few people from Tamriel have ever crossed the Padomaic Ocean in The Elder Scrolls, and the only interactions between the two continents have been military campaigns. Twice have races from Akavir invaded Tamriel - once in the First Era by the Tsaesci, and again in the Second Era by the Kamali.
Neither of these races are the Men of Akavir, though, according to an in-game Elder Scrolls book titled "Mysterious Akavir." According to this text's anonymous author, Akavir is primarily comprised of four nations - Kamal, Tsaesci, Tang Mo, and Ka Po' Tun. The Kamali people are supposedly snow demons. The Tsaesci are reported to have humanoid upper bodies attached to serpentine tails. Tang Mo, also known as the Thousand Monkey Isles, are inhabited by monkey-folk. Cat-folk are ruled by a divine Tiger Dragon in Ka P0' Tun. It is supposedly the Tsaesci serpent-folk that caused the disappearance of Akaviri Men, with some believing they were driven to extinction after being consumed by the Tsaesci. This is, however, a dubious explanation, with the idea of the Tsaesci being serpents also a subject of debate.
Following the Tsaesci invasion of Tamriel in the First Era, some remained in the west and assimilated into Cyrodiilic Empire, even becoming involved in the upper echelons of Imperial society. At one point a Tsaesci Potentate planned and succeeded in a plot to assume the Imperial throne, a saga that was recorded in a book series titled "2920, The Last Year of the First Era," which corroborates the Tsaesci being serpent-folk. The most recent contact with Akavir came during the long reign of the Septim Dynasty in the Third Era, when Emperor Uriel V attempted an invasion of the continent. The Imperial Legions landed in territory controlled by the Tsaesci, but reports never mention a lack of Men on the continent.
Because of this most recent expedition to Akavir, many believe the extinction of Men on the eastern continent to be relatively recent, if having happened at all. Legend claims the Tsaesci ate the Akaviri, but it is also possible that the serpents enslaved them. Others believe the Tsaesci are actually humanoid, meaning the Akaviri never really disappeared. Regardless, because there is so little contact with Akavir, the exact fate of the Akaviri remains one of the greatest mysteries in The Elder Scrolls, alongside the equally enigmatic disappearance of the Dwemer.