Here the 1858 Wright edition substituted the plural hands for the singular hand, the reading of the earliest (extant) sources. The first two RLDS editions also followed this plural reading, but the third RLDS edition (1908) restored the original singular, the reading of the printer’s manuscript. Elsewhere in the text we have similar examples dealing with affliction (with either the verb afflict or a similar verb like destroy, smite, or slay) for which hand can occur in either the singular or plural in the prepositional phrase “by the hand(s) of X”. If X is singular, then we always get the singular hand:
But if X is plural, we can have either the singular hand or the plural hands. In the following list, I provide the earliest extant reading; each plural case is marked below with an asterisk:
The 1830 edition changed the singular hand to hands in Alma 43:44, perhaps under the influence of the phraseology in nearby Alma 43:46 (“to be slain by the hands of your enemies”). Yet note that the similar language in Alma 51:11 reads in the singular (“which had been slain by the hand of the Nephites”), as do the examples from the small plates of Nephi and this example in the book of Mosiah. We therefore let the earliest textual sources determine whether hand should be singular or plural in the phrase “by the hand(s) of ”). See Alma 43:44 for discussion of that particular passage.
Summary: Maintain the singular hand in Mosiah 11:21, the reading of the earliest textual sources; elsewhere the text has examples of “by the hand of ”.