Between A.D. 26 and A.D. 30 the people became very wicked, and "the church was broken up in all the land save it were among a few of the Lamanites who were converted unto the true faith" (3 Nephi 6:10-14). The "chief judges and they who had been high priests and lawyers" entered into a covenant to destroy "the people of the Lord" and "to destroy the governor, and to establish a king over the land, that the land should no more be at liberty but should be subject unto kings" (3 Nephi 6:21-30). This secret society did not succeed in establishing a king over the land; but "they did destroy upon the judgment seat, yea, did murder the chief judge of the land" (3 Nephi 7:1). The people were so divided they could not agree on a form of centralized government, so "they did separate one from another into tribes, every man according to his family and his kindred and his friends; and thus they did destroy the government of the land" (3 Nephi 7:2).
“They Did Separate One from Another into Tribes”
In 3 Nephi 7:2 we find that after the murder of the chief judge in the thirtieth year, "the people were divided one against another; and they did separate one from another into tribes, every man according to his family and his kindred and friends; and thus they did destroy the government of the land."
According to John Sorenson, this picture is not of some new-fangled structure of social affiliation and governance that emerged all of a sudden when the government by judges collapsed. These [tribal] units already were deeply grounded in traditional Nephite society or they would not have emerged so universally; their existence is revealed at this point in time by default. Their earlier [importance] must have been limited by the national or state political structure. With the collapse of "the government of the land," the previously limited powers of decision-making and social control that the tribes had long exercised suddenly now expanded to fill the political vacuum. [John L. Sorenson, "The Political Economy of the Nephites," Nephite Culture and Society, pp. 217-218]
“They Did Separate One from Another into Tribes”
According to John Tvedtnes, the fact that all people knew the tribe to which they easily reverted is strong evidence of the basic tribal nature of these people: "The people were divided one against each other; and they did separate one from another into tribes, every man according to his family and his kindred and friends. . . . And every tribe did appoint a chief or a leader over them; and thus they became tribes and leaders of tribes. Now behold, there was no man among them save he had much family and many kindreds and friends; therefore their tribes became exceedingly great (3 Nephi 7:2-4). . . . We read in 4 Nephi 1:17 that there were no more "-ites" after the coming of Christ, but that all the people were united in the kingdom of God. However, this evidently has reference to political factionalism, rather than the abandonment of lineage ties. This is evidenced by the naming of these tribes in the 231st year of the Christian era as the "Nephites, Jacobites, Josephites, Zoramites, Lamanites, Lemuelites and Ishmaelites" (4 Nephi 1:35-38). That this tribal structure never changed seems to be confirmed by the order in which these identical groups are listed from the time of Jacob in the 6th century B.C. (Jacob 1:13-14), to Mormon's day 320 years after Christ's birth (Mormon 1:8-9). [John A. Tvedtnes, "Book of Mormon Tribal Affiliation and Military Castes," in Warfare in the Book of Mormon, F.A.R.M.S., pp. 308-309]