Ambitions
In order to fulfill those ambitions, he was not going to be below anyone, but he knew there was just no way he could defeat the vampire king, and even if he did manage to, it would be pointless since their society isn't like that of werewolves.
The ruler isn't based on strength but on that particular family that rules the entire race, so if he goes against the king, it will only be considered treason, and all the vampires would have turned against him.
So, he chose to create discord among the vampires, and the best way to do so was by separating the masses into two different sides, in such a way that each side would madly believe they are right and the others are evil.
The vampire king has two brothers, and one of them was the person who created civil wars among the population of vampires, and in the end, he finally managed to do what he aimed.