Notice this amazing promise that the United States would be "delivered out of the hands of all other nations." In other words, the United States would never be conquered from without. However, when we get to Third Nephi, chapter 21, It says that there will be a tremendous cleansing of America from within. That's going to be an exciting story when we get to it.
Meanwhile, here we have this present prophecy where Nephi saw the Revolutionary War and amazingly predicted the United States would win 2.300 years before it happened. Notice that Nephi saw the refugee Gentiles or American settlers prospering in the land. In 3 Nephi 21:4 it says these highly blessed Gentiles will set up the first free people in modern times, and in 3 Nephi 20:27 it says this nation will be mighty above all other nation in the world. Of course when these prophecies appeared in the Book of Mormon, which was published in 1830, it must have sounded like extravagant boasting. In fact there were three empires in Europe who considered the struggling American republic to be relatively insignificant. Only in this past century has the United States begun to fulfill its Book of Mormon destiny of becoming mighty above all other nations in the world.