Tamriel (TES) faces the Blight (DA:O)

The timeline is at the end of the events of Skyrim, but only after the two main storylines have been completed (The Civil War and Dragonborn). Whether Uflric or Tullius has won is up to you.

The Darkspawn have been amassing their numbers in the great subterranean expanses beneath Skyrim, taking over Dwarven ruins, caves, and things of that nature. Just when the Empire is starting to take notice, the Blight begins. An Archdemon emerges, army and all, from beneath the city of Markarth. The city and its inhabitants are slaughtered, women taken to be broodmothers, and Markarth becomes the first corrupted city, the Ruins beneath it becoming the Archdemon's lair.

The Dragonborn, through an Elder Scroll, was given the knowledge on how to initiate Grey Wardens and thus kill the Archdemon.

R1: Does the Blight take all of Skyrim? R2: If they don't, how far do they get? R3: If they do, can they conquer all of Tamriel? If not, how far do they get?