Deuteronomy 7:22

Put out those nations - by little and little - The Israelites were not as yet sufficiently numerous to fill the whole land occupied by the seven nations mentioned Deuteronomy 7:1 . And as wild and ferocious animals might be expected to multiply where either there are no inhabitants, or the place is but thinly peopled, therefore God tells them that, though at present, by force of arms, they might be able to expel them, it would be impolitic so to do, lest the beasts of the field should multiply upon them.