A scholar explained the meaning of “the isles of the sea”: “Nephi not only refers to the isles of the sea as the location of other remnants of the house of Israel, but he also indicates that he and his people were then living upon an ‘isle of the sea’ when he quite clearly is referring to the great land mass known as the American continent. (2 Nephi 10:20–21.)” (Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon [1976], 121).
For more information on the scattering of Israel, refer to “Brief History of the Scattering of Israel” in the appendix (page 415).