Every race that decided to take part in the Great War had some reason, it was obvious.
Sven's reason was enough to give up the opportunity to rule an entire world in the future for it. He stood on Nameless King's side and risked everything for it. If he succeeded he could escape a boring world, a utopia that would slowly rot, if not, he would lose everything.
Alucard and Gael had a somewhat similar situation, however, for them the main reason was simply that they wanted to help the Nameless King. They wanted the world to be interesting, if one person controls everything then their wish would not be realized.
Polosa had a simple lust for power and territory. She wanted more out of her life than just being the Ruler of a pacifist race whose members don't want to fight.
