The Book of Mormon is clear that the New Jerusalem would be in place before the Book of Mormon came forth. Joseph Smith missed this fact and hi-jacked the idea for his own use as demonstrated here in Article of Faith #10:
We believe in the literal gathering of Israel and in the restoration of the Ten Tribes; that Zion (the New Jerusalem) will be built upon the American continent; that Christ will reign personally upon the earth; and, that the earth will be renewed and receive its paradisiacal glory. (Article of Faith #10)
Mormons leaders have prophesied against the real New Jerusalem (United States government) even calling her “Babylon” and taking “oaths of vengeance” against her in earlier temple ceremonies (see Temples).