What is the primary motivation behind the Invincible War?

The primary motivation behind the Invincible War is the Viltrumite Empire's long-standing agenda of galactic conquest and their belief in their own racial superiority. Thragg, specifically, aims to reclaim Earth for the Viltrumites and impose their rule, viewing humans as a primitive species to be dominated. He also seeks revenge for past defeats and to solidify the Viltrumite dominance across the galaxy.