I'll talk about the Black Hand in more detail later on.....
Okay, now, as to WHY he wants to destroy so many towns, it is because that is how he dervives his energy, the slaughter of many. (He absorps their energy.) And, watch, there will be something special about each and every one of these towns. Like, a shrine will be in place there, or something else that creates much spiritual energy. That is because that AT LEAST triples the amount of energy he receives.
However, this is also his weak point. If he does not destroy the needed number of villages/lives, then he will die. It is the energy of the deaths that keeps him alive.