Kill them all!!!

Deuteronomy 20:17 says, "But thou shalt utterly destroy them; namely, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites, and the Jebusites; as the LORD thy God hath commanded thee:"  If God killed everyone in the flood why would there be other people on the earth?  Why would he want them killed? These people had to have been born from the Israelites, so why would a loving God forsake them and not speak and guide them like he did others?