Long ago, there was a ferocious war between dragons and humans alike. It got to the point where both races were near extinction. Thus the pact of the leaders of old was formed. The second born of royal birth (even a dutches or a lady of some other high rank) was to be given to the dragons as a human sacrifice. In exchange, the dragons left the rest of the humans alone. No one new what happened to them. No one but the dragons.