Board Thread:Lore Discussion/@comment-13417807-20130726023954/@comment-69.123.217.197-20150304220234

Nebenthe wrote: The Thu'um is the only thing that the humans (Nords) potentially have over the elves, and the Thalmor want to take that away from them.

I think the Thalmor want to become the next Ayleids. The Thalmor want to destroy Nirn, as they believe this will restore them to their previously divine state as et'Ada. Whether or not destroying creation will actually return them to that state is debatable, but that is what they believe, and what they work towards.