This table compares Joseph Smith's Wentworth letter with Orson Pratt's 1840 pamphlet.
Joseph Smith's article titled "Church History," commonly referred to as the Wentworth letter, was published in the Times and Seasons in March, 1842.
As explained in the Historical Introduction, the Wentworth letter appears to borrow considerable material from a pamphlet published by Orson Pratt in 1840. (Orson Pratt in turn had borrowed from Oliver Cowdery's Letters VII and VIII.)
The Joseph Smith Papers published Pratt's pamphlet and shaded parts of the text that correspond to the Wentworth letter.
Orson Pratt's pamphlet set out at length his hemispheric theory of Book of Mormon geography, with Lehi landing in Chile, Mulek landing in North America, etc.
By comparing the two documents, it is apparent that Joseph Smith made several minor but significant changes/corrections. One of the most important is that Joseph replaced Pratt's hemispheric model with the simple declaration that "The remnant are the Indians that now inhabit this country."
Joseph's statement is consistent with D&C 28, 30 and 32, the New York Cumorah, the "plains of the Nephites" in Ohio, Indiana and Illinois, etc.
By contrast, Orson Pratt's hemispheric model was based on pure speculation that Joseph never endorsed and instead explicitly replaced in the Wentworth letter.