How it was that God foretold to Abraham that Israel would have to drive out ten nations.
When the Lord was speaking with Abraham about the future (a point which you did not ask about) we find that He did not enumerate seven nations, but ten, whose land He promised to give to his seed. 1356 And this number is plainly made up by adding idolatry, and blasphemy, to whose dominion, before the knowledge of God and the grace of Baptism, both the irreligious hosts of the Gentiles and blasphemous ones of the Jews were subject, while they dwelt in a spiritual Egypt. But when a man has made his renunciation and come forth from thence, and having by Gods grace conquered gluttony, has come into the spiritual wilderness, then he is free from the attacks of these three, and will only have to wage war against those seven which Moses enumerates.
Cf. Gen. xv. 18-21.