The Oblivion Crisis (Dark Heritage)

Prologue
With the magical wards against Oblivion failing, the otherworldly dimension found little resistance to invade the mortal realm. Molag Bal, Mehrunes Dagon and Malacath, also simply known as "the Three" or the Prime Evils, commanded legions of Daedra through the Oblivion Gates from their own respective corner of Tamriel. Molag Bal entered with his armies through a gate south of Chorrol, Cyrodiil. Mehrunes Dagon entered from a gate spawned in the fiery chasm of Dagoth Ur. And Malacath came from the cold reaches of northern Skyrim, causing the destruction of Winterhold. Their primary objective was to secure the mortal realm and reach the Throat of the World, the sole link between the mortal world and Aetherius, in order to combat the Aedra for total universal domination.

Event
There was no warning against the upcoming threat and most of Tamriel was taken by surprise by the sudden attack of Oblivion. Numerous cities, forts and settlements fell during the course of a week, among them Winterhold, Dawnstar, Chorrol, Kvatch, Hackdirt, Ald'Ruhn and Ghostgate.

A desperate attempt was made by several local troops and armies surrounding the affected cities to try and push the Daedra back, but they all ultimately failed and were slaughtered, some of them resurrected to fight for Oblivion's cause. As the news reached the capitals of the surrounding nations, an ambitious effort was made by the commanders Modryn Oreyn, Eydis Fire-Eye and Varus Vantinius to summon a global call-to-arms with immediate effect. The estimated number of people enlisting or joining the fight against the Daedric invasion remains unknown, but it is said that the numbers were over millions of participants willing to defend their homeworld.

In the destructive wake of the Daedric Princes' path to reach the holy mountain the Throat of the World, they left burning villages and massacred citizens. While the united armies of Tamriel had some success in reclaiming sacked cities and villages from the Daedra stragglers, there was no way for them to stop the legions of Oblivion from reaching the holy mountain. The two sides eventually met on the tundra outside of Whiterun. The Three having combined their forces came from the north, while the united armies of Tamriel pushed in from the south. The two worlds clashed in what would be remembered as the most devastating loss of lives in Tamrielic history.

When all hope seemed lost and the Daedra were about to breach the slopes of the holy mountain, the Aedra directly interfered as Talos, the Aedra of War and Governance, and Stendarr, the Aedra of Mercy and Righteousness, joined forces with the mortals. From that moment onward the tide was turned as the vast numbers of Daedra was completely decimated and the Three brought to submission.

Aftermath
As the Oblivion threat was vanquished, the wards against Oblivion strengthened and the Oblivion Gates were destroyed, the Three were taken into magical custody by the Aedra. Seeing as both Aedra and Daedra are immortal spirits in origin, the Aedra knew that it was impossible for them to completely destroy their demonic counterparts. Instead they decided to rob the Three of their corporeal form and trapped their essences inside soul gems. These they handed to various cults and monastic orders of Mankind for safekeeping, to ensure that the Prime Evils would never walk the mortal realm again.