Deuteronomy 7

Moses' instructions to the Israelites continue in this chapter, and focus in on God's greatness and power - specifically as it relates to His bringing Israel out of Egypt and into the promised land. They are also commanded to absolutely wipe out the current occupants of the land, down to each person, along with their idols and objects of worship. Moses also notes that all of their enemies won't be destroyed at once, lest wild animals srpead uncontrolled and cause problems - which is something I would not have thought about as a problem, but it makes sense. That region of the world isn't huge, but still it would be hard to fully occupy and civilize with a host of only 600,000 men and their families (maybe two or three million total people, at most).