The LORD your God will drive out these nations before you little by little. You will not be enabled to eliminate them all at once, or the wild animals would multiply around you.
KJV
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.
ASV
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.