In this verse the 1841 British edition introduced two secondary readings. The first was the accidental addition of the before east, creating the very strange noun phrase “the east of the river Sidon”. Even more strange is that this awkward reading was maintained in the LDS text until the 1920 edition. Whenever a cardinal direction is the head noun in a prepositional phrase and the direction is immediately followed by the preposition of, the definite article the occurs before the direction:
as the head noun in a prepositional phrase (a sampling from 20 occurrences)
But when the cardinal direction acts as the subject complement (as here in Alma 2:15) or when it postmodifies another noun, the direction always occurs without the the:
as the subject complement (a sampling from 8 occurrences)
as the postmodifier for a noun (2 occurrences)
Of course, these results correspond to modern English usage.
The second 1841 change in this passage was also accidental—namely, the loss of the preposition of from “the land of Zarahemla”. As noted under 1 Nephi 17:7, either reading, with or without the of, is theoretically possible. But it actually turns out that in the original text of the Book of Mormon there are only instances of “the land of Zarahemla” (105 times). Here in Alma 2:15, the 1920 LDS edition restored the of to the LDS text. Elsewhere there are four cases where of has been accidentally omitted from “the land of Zarahemla”. In each of these other cases, the omission was limited to a single textual source:
passage source of omission
For discussion, see each passage. The critical text will maintain the consistent use of of in the phrase “the land of Zarahemla”, although theoretically “the land Zarahemla” is possible. For discussion of the phrase “the land (of ) X”, especially when X is the name of a person, see under Alma 27:23 regarding the phrase “the land (of ) Nephi”.
Summary: Maintain the consistently used phrase “the land of Zarahemla” in Alma 2:15 and elsewhere in the text; also maintain in Alma 2:15 the word east without any preceding the (“which was east of the river Sidon”).