Deuteronomy 7:22

“And the Lord thy God will put out those nations before thee by little and little, etc.] Which is observed for their encouragement, who seeing that all were not destroyed at once, might fear the work would never be thoroughly accomplished; (see <022330>Exodus 23:30), thou mayest not consume them at once; though it was in the power of their hands to do it, there being some wise reasons for sparing them awhile, at least for not cutting them off all at once, and one follows: lest the beasts of the field increase upon thee; through so many places being waste without inhabitants, and there being none to destroy these creatures; and who therefore in course would become more numerous, and so more…”

“lest the beasts of the field increase upon thee--(See on Exo 23:29). The omnipotence of their Almighty Ruler could have given them possession of the promised land at once. But, the unburied corpses of the enemy and the portions of the country that might have been left desolate for a while, would have drawn an influx of dangerous beasts. This evil would be prevented by a progressive conquest and by the use of ordinary means, which God would bless. Next: Deuteronomy Chapter 8”

“put out: Heb. pluck off thou mayest: As the Israelites were not yet sufficiently numerous to fill the whole land occupied by these nations; and as wild and ferocious animals might be expected to multiply where the place was but thinly peopled, therefore God informs them that their extermination from before them should be gradual. Haynes says, "The approaching to Cana, at the close of the day, as we did, is at once terrifying and dangerous. The surrounding country swarms with wild beasts, such as tigers, leopards, jackals, etc., whose cries and howling, I doubt not, would strike the boldest traveller, who had not been frequently in a like situation, with the deepest sense of horror." Exo…”