Helaman 11:24

And it came to pass that in the eightieth year of the reign of the Judges over the people of Nephi, there were a certain number of the dissenters from the people of Nephi, which had some years before gone over unto the Lamanites, and took upon themselves the name of Lamanites; and also, a certain number which were real descendants of the Lamanites, being stirred up to anger by them, or by those dissenters, therefore they commenced a war with their brethren.

In the eightieth year the judges ruled over the Nephites, something happened. Some Nephites had left their people years before. They had joined the Lamanites. They took the name Lamanite. These people got some real Lamanites angry. So the Lamanites started a war against their own people.

In the eightieth year of the judges’ rule over Nephi’s people, some Nephite defectors—ones who’d left years earlier to join the Lamanites and taken on their name—stirred up anger among some actual Lamanite descendants. Together they started a war against their own people.