The mention that "the Lamanites began to increase in riches and began to trade one with another" (Mosiah 24:7) enhances the meaning and purpose of the "language of Nephi" which was being taught. We learn in Mosiah 24:6 that "they taught them that they should keep their record, and that they might write one to another." The institution of a common writing system must have been the key to commerce between many different cultures because trade and riches increased thereafter. [Alan C. Miner, Personal Notes]
“The Lamanites Began to Trade with One Another”
In Mosiah 24:7 Mormon writes that "the Lamanites . . . began to trade with one another." However, Brant Gardner notes that trade is a part of virtually all societies. Donald E. Brown has examined multiple populations of the world to attempt to extract those things that we, as humans, hold in common. Among those things so prevalent among virtually all societies that may be deemed a "human universal" is trade. That the Lamanites may have become even better at trade due to some of the knowledge from the Amulonites is quite possible. That they had never traded before this time is not at all possible. [Brant Gardner, "Book of Mormon Commentary," [http://www.highfiber.com/~nahualli/] LDStopics/ Mosiah/Mosiah24.htm, p. 9]