According to Abel, the humans that were washed ashore in the land of vampires were greedy. Even after being welcomed by vampires and provided with their necessities, humans plotted to sell this information once they were outside the land for the money or simply for added manpower.
Vampires were strong and terrifying creatures. Having one was worth a unit of human soldiers. Subduing them all meant having the world at their feet. It may be ridiculous to think how humans could even consider they could attain such a feat, but humans were humans.
They were creatures whose ambition was limitless. The sky's the limit.
That was when Soran, the man Abel admired, slaughtered every human who came with him. Making a mountain of human corpses, he stood on top of them until the vampires came from the permeating scent of blood and death.
