Deuteronomy 7:20-22

Moreover the LORD thy God will send the hornet among them, until they that are left, and hide themselves from thee, be destroyed. Thou shalt not be affrighted at them: for the LORD thy God is among you, a mighty God and terrible. And the LORD thy God will put 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.