The initial author was Omni, but several others were charged with keeping the record as time passed, though few made significant contributions. In verse 5 it is explained that "the more wicked part of the Nephites were destroyed." There is little detail about the destruction, except to say that the Lord did visit them in great judgment because of their wickedness.
Chemish speaks of many wars between the people of Nephi and the Lamanites.
Amaleki speaks of the then current Nephite king, named Mosiah. As had happened previously, the Lord told the king (who appears to be a spiritual leader (prophet) as well as a secular leader) to lead the righteous Nephites out of the land of Nephi to a new place. They discover a group of the Mulekite people whose ancestors had also come from Jerusalem, but after it was attacked by the Babylonians. These people, however, did not bring religious or historical records with them which had two results- they had lost their religion, and they were unable to preserve their language from generation to generation. These people are known as the people of Zarahemla (their then current king, and also the name given to the land. Mosiah arranges for the people of Zarahemla to be taught the Nephite language, and Zarahemla is able to recount to him their oral history.
The two groups of people united themselves with Mosiah as their king, and they are all known as Nephites.
The first mention of the Jaredites is found here as well. A large stone is found with writing on it. Mosiah is able to "interpret the engravings by the gift and power of God." It tells of a man named Coriantumr and the downfall of his people. Their history is recounted more fully in the Book of Ether.
Mosiah, the king dies and his son, Benjamin, becomes king. There is a war between the Nephites and Lamanites, which by this time is nothing new.
Amaleki then describes some of the Nephites who wish to return to the land of Nephi, apparently in an attempt to reclaim it. At the time Amaleki stops writing, he has not received word of them, including his brother who is among them.
Amaleki closes with some words about Jesus Christ, asserting that his words are true and that it is his intent to help others come unto Christ. He states at the close of the book that, having no descendants to carry on the record-keeping, he will give the records to King Benjamin.