Omni 1:16 - 1:20

Omni 1:16 And they journeyed in the wilderness, and were brought by the hand of the Lord across the great waters, into the land where Mosiah discovered them; and they had dwelt there from that time forth.

Mosiah learns that these people were lead through the wilderness from Jerusalem and traveled across the sea as did Lehi’s family. Where they landed in the promised land they had never settled in any other areas of the promised land.
[I assume these people took somewhat the same route as did Lehi. Wonder what their experiences were in the wilderness and did they also had the same kind of guidance by angels and instruction in building a ship?]

Omni 1:17 And at the time that Mosiah discovered them, they had become exceedingly numerous. Nevertheless, they had had many wars and serious contentions, and had fallen by the sword from time to time; and their language had become corrupted; and they had brought no records with them; and they denied the being of their Creator; and Mosiah, nor the people of Mosiah, could understand them.

These people had multiplied to become a large population in this area. They had had their conflicts and internal strife's which brought death to many in their civil wars. Since they had brought no records with them, like the brass plates, their religious beliefs had changed to the point that they did not believe in a God anymore. In addition, their language had changed over time as does all language that is not written down to the point that the people of Mosiah could not understand them.

Omni 1:18 But it came to pass that Mosiah caused that they should be taught in his language. And it came to pass that after they were taught in the language of Mosiah, Zarahemla gave a genealogy of his fathers, according to his memory; and they are written, but not in these plates.

Mosiah now teaches these people his dialect so they could now understand and communicate with each other. The genealogy of this people are now written down on plates but not the ones we are reading from now.
[It is interesting that these people learn Mosiah’s language and not the other way around. I think one reason of this adoption of Mosiah people's language is so that the Mulekites would have the ability to read the scriptures and know how to add to them their own experiences. It must have been because of the prophets and the power of Mosiah that these people want to learn Mosiah’s ways and government and language.]

Omni 1:19 And it came to pass that the people of Zarahemla, and of Mosiah, did unite together; and Mosiah was appointed to be their king.

These two peoples unite under Mosiah and he is appointed king over both.
[Wonder if there was any dissension by some these people who may have wanted one of their to be king? It must have been very evident that Mosiah leadership abilities and their organization of Mosiah’s people that these people could see who would be the better choice to rule over all.]

Omni 1:20 And it came to pass in the days of Mosiah, there was a large stone brought unto him with engravings on it; and he did interpret the engravings by the gift and power of God.

During the reign of Mosiah, a stone was shown him that had engravings on it. Mosiah interpreted the writings by the gift and power of God.
[They could not be read as they were of any unknown language. It takes a “sear” to interpret such things.]