And this is the account of the wars and contentions among the Nephites, and also the wars between the Nephites and the Lamanites; and the fifteenth year of the reign of the judges is ended.
And now, as I have spoken concerning these plates, behold they are not the plates upon which I make a full account of the history of my people; for the plates upon which I make a full account of my people I have given the name of Nephi; wherefore, they are called the plates of Nephi, after mine own name; and these plates also are called the plates of Nephi.
Nevertheless, I have received a commandment of the Lord that I should make these plates, for the special purpose that there should be an account engraven of the ministry of my people.
Upon the other plates should be engraven an account of the reign of the kings, and the wars and contentions of my people; wherefore these plates are for the more part of the ministry; and the other plates are for the more part of the reign of the kings and the wars and contentions of my people.
1 Nephi 9:2-4
The large plates were for the contentions. The small plates were for the ministry. We just read of the ministry of Ammon and his brethren. And now we’re reading about the wars! Why are they both on the same plates? Well,
and these plates are full
That was the end of the Small Plates. From then on, everything went on the Large Plates. Towards the end of the Large Plates, the two were complied by Mormon and Moroni.