Deuteronomy 7:20-22

Moreover Jehovah thy God will send the hornet among them, until they that are left, and hide themselves, perish from before thee. Thou shalt not be affrighted at them; for Jehovah thy God is in the midst of thee, a great God and a terrible. And Jehovah thy God will cast out those nations before thee by little and little: thou mayest not consume them at once, lest the beasts of the field increase upon thee.