As you attack these nations, the LORD will force them out little by little. He won't let you get rid of them all at once--if he did, there wouldn't be enough people living in the land to keep down the number of wild animals.
There are still some nations left, but the LORD has promised you their land. So when you attack them, he will make them run away. I have already divided their land among your tribes, as I did with the land of the nations I defeated between the Jordan River and the Mediterranean Sea.