Within The Elder Scrolls franchise, the Argonian race and their home province of Black Marsh are shrouded in mystery. Much of their history, society and traditions are entirely unknown to both the player and the wider world of Tamriel. What little is known about the race comes from their interactions with outside forces.
One such example is the Argonian invasion of Morrowind, also known as the Accession war. This bloody and brutal conflict occurs between The Elder Scrolls IV: Oblivion and The Elder Scrolls V: Skyrim and ties into several aspects of the fifth title in the franchise.
The Argonian province of Black Marsh sits on the border of Morrowind, home of the Dunmer. When the first Dunmer explorers (originally named Chimer) ventured into Black Marsh and encountered Argonians, they viewed them as sub-human creatures, but their ability to survive in the incredibly harsh climate of their homeland made them perfect for labor. The Dunmer began a long tradition of enslaving the Argonian people. The slavery of the Argonians began before the First Era, and continued for generations, despite the semi-frequent slave uprisings that were repeatedly squashed.
When the Empire began expanding in the Second Era, the Argonians gained an understanding of the concept of land and borders. While under frequent attack from Dunmer raiding parties to acquire more slaves, the Argonians also fought against the Empire for both their freedom and recognition of their homeland. The Empire would eventually grant them such recognition, giving the province its name of Black Marsh, but the Dunmer continued to enslave its inhabitants.
The Empire would outlaw slavery entirely, but Morrowind would ignore this edict and continue to enslave the race, as they still viewed them as lower class creatures unworthy of the same respect they would show each other. The Argonians began a war against the Dunmer known as the Arnesian War, which was lost to the more advanced race of Morrowind. The war led to the Argonians losing many provinces of Black Marsh to the Dunmer and being seen as even lower than they were before. Eventually, some portions of Morrowind would cease trading in Argonian slaves, but others, such as areas controlled by House Telvanni, refused to follow suit.
During the Oblivion Crisis, the Argonians were warned of the coming catastrophe by the mysterious sentient Hist Trees. The Argonians prepared themselves for the crisis and ended up swarming into Oblivion itself when the gates opened, overwhelming the Daedra. Incredibly, the Daedra would close the gates themselves to save themselves from the relentless assault. This counter-offensive was led by a faction of Argonians known as the An-Xileel, who rallied the natives of Black Marsh. The Argonian people finally felt in a position of strength; while the rest of Tamriel was still reeling from the Oblivion Crisis, the An-Xileel began an invasion of the weakened Morrowind.
While the exact motivations behind the invasion are unknown, there are many reasons that can be inferred. For one, the Argonian people had suffered racism, oppression and slavery from the Dunmer for generations and likely wanted to avenge their losses. In addition, the loss of so much of their homeland to the Dark Elves in the Arnesian War was a bitter pill to swallow for the natives of Black Marsh, and reclaiming those lands was a huge priority. Some conspiracies claim that the Thalmor were responsible for the Argonian invasion, and others imply that the Hist themselves ordered the Argonians to attack.
The Argonians killed thousands as they advanced through Morrowind. The southern part of the province that bordered on Black Marsh was utterly devastated by the invading forces. It was only the combined power of House Redoran's forces that managed to finally halt the Argonian advance. Many Dunmer fled the province in terror, ending up across Tamriel. In the previous year, following the eruption of Red Mountain, the High King of Skyrim offered the Dunmer the island of Solstheim as a refuge. Following the Accession War, the High King once again extended an invitation to the Dunmer. Many would take this offer, settling on Solstheim and other provinces of mainland Skyrim. When the Dragonborn arrives on Solstheim during the events of Skyrim's Dragonborn DLC, it has been gifted to the Dunmer in its entirety and has become a colony of Morrowind.