In this passage, Joseph Smith’s editing for the 1837 edition treats people as a plural; thus he changed “a people which was” to “a people who were”. The plural usage for people is characteristic of Joseph’s editing for the 1837 edition (as is his change of which to who when which refers to people); this same editing is found in the following example where Joseph Smith edited an original “this people which is” to “this people who are”:
But there are still two instances of semantically singular people in the text:
These expressions are, to be sure, fairly awkward for modern speakers of English, but the use of this in each case supports the use of the singular verb is.
In his editing for the 1837 edition, Joseph Smith typically made the change from which to who (or whom) when the antecedent was people, but there are ten instances where he didn’t, most of which are found at the end of 2 Nephi and at the beginning of the book of Jacob, as in these examples:
The critical text will, of course, restore all instances of original which. For a complete discussion, see under which in volume 3.
Summary: Restore in 4 Nephi 1:36 the original which and the singular was in the relative clause that modifies people; such usage is characteristic of the original Book of Mormon text.