Mosiah 25

Mosiah 25 is the chapter that establishes the Nephites and Lamanites again as the two main peoples referred to in the Book of Mormon.  Splitting off had occurred way back in Omni when Zeniff and his people left.  But now, King Limhi and his people, along with Ammon, are back in Zarahemla as are Alma and those who followed him.  (These two groups are both descendants of the Zeniff group.) They along with the Nephites that remained in Zarahemla and the Mulekites that built Zarahemla are now joined together and referred to as Nephites.  Mosiah 25:13 says:

"And now all the people of Zarahemla were numbered with the Nephites, and this because the kingdom had been conferred upon none but those who were descendants of Nephi."

Then, Alma establishes the church among the people and baptizes many people.  And so, the way that I normally think of the people in the Book of Mormon is set up...There are Nephites and Lamanites (much more Lamaites than Nephites).  And there is a leader of the church in the land--Alma.