Akatosh is infudiated that talos is not being worshipped as a divine anymore. So he allows the daedra into tamriel. The thalmor (who are secrer daedra worshippers) predicted this would happen. The thalmor chose talos as the god to ban worship upon because it would cause a large uproar, and likely start riots/rebellions within the empire, thus weaking it. The thalmor were right, as many people (except rebels) say "by the eight" instead of "by the nine". so back to the daedra, the dremora invade tamriel yet again, and the thalmor attempt to make a bargain with clavicus vile. This does not work out, and the dremora destroy almost all of the high elf homeland. Thus the thalmor is forced into an uneasy alliancd with the empire/stormcloaks to rid nirn of the daedra yet again.
This is my theory based on the book, "The Amulet of Kings". I believe it can be found in Israns room in fort Dawnguard. Let me know your thoughts.