Deuteronomy 7:20-22

Moreover, the LORD your God will send the hornet among them until even the survivors who hide from you have perished. Do not be terrified by them, for the LORD your God, who is among you, is a great and awesome God. The LORD your God will drive out those nations before you, little by little. You will not be allowed to eliminate them all at once, or the wild animals will multiply around you.