Here Joseph Smith removed the definite article the since in English we expect the phraseology “to establish peace between X and Y”—that is, without the definite article the. If peace is postmodified by an of-prepositional phrase, we typically get the before peace in the Book of Mormon text:
Moreover, there are three occurrences of “to keep the peace” without any postmodification, and in each case the definite article the has been retained:
Of course, the verb here is keep rather than establish, and we expect the the in that case.
There is no other example in the text quite like this one in Helaman 2:1. Here Joseph Smith’s editing seems to deal with a question of style rather than grammar. The critical text will restore the original the.
Summary: Restore in Helaman 2:1 the definite article the before peace since the earliest text read this way and there is really nothing wrong with the expression “to establish the peace”.