The Oblivion Crisis, also known as the Great Anguish, was a total war between the Daedra and the population of Tamriel. Uriel Septim VII and all of his known heirs were assassinated. Shortly afterward, Oblivion Gates to the Deadlands opened across Tamriel and Daedra poured out as the result of a fanatical cult of worshippers of Mehrunes Dagon known as the Mythic Dawn. Widespread devastation and casualties resulted across entire provinces. The Daedra besieged Skyrim, and laid waste to the Old Holds. In Black Marsh, the Hist called back many Argonians to fight off the Daedra. The Daedric commanders closed many gates to stop the united Argonians from entering. In Cyrodiil, the city of Kvatch was entirely destroyed. The Empire earned the hatred of the Dunmer by pulling Imperial forces out of Morrowind during the crisis in order to better protect Cyrodiil. The Empire was near collapse, but Uriel VII's illegitimate son, Martin Septim, ended the invasion with the help of a mysterious hero, but the cost was enormous. Martin, the last of the Septim bloodline, sacrificed himself and the Amulet of Kings to become Akatosh's Avatar and cast Mehrunes Dagon back into Oblivion. This event marked the end of the Third Era and the beginning of the eventual disintegration of the Third Empire.
 Major Battles
- Sack of Kvatch, 3E 433. Oblivion gates are opened outside Kvatch, from which a horde of Daedra and a huge siege crawler emerge to overwhelm the guard and sack the city. Much of the population was killed, including Count Ormellius Goldwine and Saint Jiub. After the city is occupied by the Daedric forces most of the gates are closed, leaving only one lesser gate blocking the city's gates. This gate is eventually closed by an unknown hero who then leads the remaining city guard to retake the city.
- Sack of Ald'ruhn, 3E 433. The city of Ald'ruhn was destroyed by the Daedra. In an attempt to defend the city the Redoran resurrected the Ald Skar Emperor Crab, which also fell.
- Sack of the Crystal Tower, 3E 433. The Crystal Tower on the Summerset Isle, the bastion of all magical learning before the Arcane University was built, was destroyed by Mehrunes Dagon's invading Daedra, despite the efforts of the powerful Altmer wizards.
- Battle of Bruma, 3E 433. Martin Septim led an army of Cyrodilic city guards to victory over the invading Daedric hordes. A statue was erected within the city's walls, in honor of the lone hero who charged into Oblivion in order to shut the great gate and prevent the destruction of Bruma.
- Battle of the Imperial City, 3E 433. High Chancellor Ocato, Martin Septim, his Blades and Imperial Legionary escorts fought their way through an Oblivion-sieged Imperial City. During this battle dozens of Oblivion Gates opened up around the City and the Daedric Prince Mehrunes Dagon himself appeared in the besieged city, marking the fall of the barriers between Oblivion and Nirn. The battle ended when Martin Septim, in a desperate last ditch effort, shattered the Amulet of Kings and became the Avatar of Akatosh. The Avatar banished Dagon back into Oblivion, ending the Oblivion Crisis. The Avatar turned to stone, killing Martin, but also leaving a permanent reminder of Martin's sacrifice.