The story of Nehor reads like a small footnote or blip on the radar of Nephites history, while the story of Amlici and the King Men continues to impact Nephites history throughout the Book of Alma and elsewhere. Nevertheless, I think these two events are actually closely connected to each other.
A major portion of what had held the Nephite nation together since the merger with the people of Zarahelma was a commonly held faith. It’s not sure what percentage of the people formally belonged to the Church of God, but it does seem likely that they were unified in the very least in their beliefs in the God of Abraham, Isaac, and Jacob. This is why the Nephites are referred to as the people of God in this chapter.
King Benjamin sought to unite his people under a single common faith because he understood that this would lead to a United and harmonious people. And for at least a generation this worked well. But as the younger generation grew and fell away to Nehor’s teachings, something seems to shift culturally and socially.
Before Nehor, the previous heretic in the Book of Mormon was Sherem. Sherem denied Christ but still operated under the framework of the Law of Moses. Nehor is the first to shake that paradigm. His idea that religious authority comes from the people and that God ultimately will save all regardless of belief allowed for radical innovations and departures from traditional notions of faith. I believe his teachings inspired the King Men to revolt against their leaders and to diverge from the people of Nephi. If religious authority came man rather than God, then there was far less reason to stay attached as a common people with common religious and political leadership.
The move towards the rule of judges may have unintentionally accelerated this shift as well. Without a common sacral and political leader, the people would have felt less bound together by common leadership and authority.