Dear dmfew,
I would like to remind you that David is a Jew. The Jews were and still are God's chosen people. When the Ammonites, Moabites, Amalekites, Hittites, Syrians, Edomites, and all the others, decided to go against God people, by their own accord, God needed to protect his people from the attacks by all these people. He did this so the Jews would be able to live and carry on his ministry. All of the previous civilizations weren't very civil. They practiced witchcraft, sacrificed humans, drank blood, burned their babies to death on the hands of Red-Hot Idols, They were sexually immoral and their ways where abhorrible. God is merciful, but when there is a cancer in the body, it must be removed. David's enemies wanted to destroy God's people. It was either them or the Jews.