Board Thread:Lore Discussion/@comment-25343239-20150128215539/@comment-86.130.80.150-20150129125721

Sooo this is how i see it...

Deadra could always appear but not in great numbers or strength and usually needed a shrine or some object, back in Morrowind they would mostly appear (note mostly) around the ruined Deadric Shrines burial sites or places where worshipers summoned them. At the start of Oblivion when the Emperor was killed and no Septim took his place that was no longer the case the barrier between the mortal and Deadric realm became weak this allowed Dagon to use the Oblivon Gates to send whole armies of Deadra to actually assault citys in a organised manner. As said above at the end of the Obivion Crisis Sean Bean... i mean Martin Septim's sacrifice restored the barrier so no army could cross over again.

Spoilers for Dragonborn! A good example of the limit of even a Deadric Prince's power was when Hermaeus Mora wanted the Skaal Shamen he had manipulate the player to get the Shamen to open the Black Book they can talk to mortals in visions or dreams and even send them mad but its very hard to physically manifest themselves in the mortal realm Sanguine kinda does (somehow) at the end of his quest in Skyrim but he's only a normal Deadra so probably not his true full powered form (like how Dagon could appear in the end of Oblivion).

Also Deadra can't be killed or really permanent harmed they just get sent back to whatever Deadric plane they came from and reform (it can take hundreds of years though).

With the Princess of Dusk and Dawn (Azura) as the Chimer/Dunmer people all worshiped her she probably had much more power over them and their land which is how when Vivec and the Tribunal betrayed her she could turn the whole race of Chimer in to Dunmer (and how she maybe turned a few Bosmer in to the Khajiit race).

As for the Trial of Vivec (again my personal opinion and a bit ranty sorry) i hate all this CHIM stuff i know a lot of people think its great but i see it as the TES version of the Deus ex Machina trope a lot of it came from a former TES developer but anyway the Trial actual says at the end maybe Vivec used CHIM banished Azura and sealed her realm or maybe she did it herself, i like to think all Vivec did was anger Azura (again opinion!). Nobody puts Azura in a corner.