Okay so… Sauron is a bit more to it. Melkor/Morgoth, his Valar, sung into existence evil into middle earth during the song of creation, by joining in with dissonance. In doing so he insured that his power and his being would forever be tied to Middle Earth, manifested through the creation of evil itself. Evil will never leave middle earth because of this.

Sauron wants to continue this endeavor, and seeks to overthrow the maiar in middle earth (the white, grey, brown, and blue wizards) and rise to the status of a valar. He then wants to overthrow the Valar’s influence over middle earth, as they were the ones that ultimately slew his master, Morgoth.

This is still ultimately foolhardy, as he then would have to contend with Eru Illuvitar, literally god.