American Continent Empty?

The Improvement Era, July 1940, Vol. 43, no. 7, pg 396; “The Lord took every precaution to see that nothing might interfere with this posterity of Joseph in working out their God-given destiny and the destiny of America. He provided, and so told Lehi at the very beginning of his settlement, that… it is wisdom that this land should be kept as yet from the knowledge of other nations… The Lord so kept the land for a thousand years after Lehi landed. He so kept it in His wisdom for another thousand years after the Nephites were destroyed, perhaps to give the Lamanitish branch another chance.” – J. Reuben Clark

http://archive.org/stream/improvementera4307unse/improvementera4307unse_djvu.txt

So what about all the people that were already living here when the anointed Joseph was born? That kind of messes up 2 Nephi 1:8 which promises America would be empty.