Lamanites is a term used in the Book of Mormon and was originally used to describe the descendents of Laman, the first-born son of Lehi (a prophet who was led by God out of Jerusalem to “the promised land” or the Americas), and his followers. In Mosiah 10:11-17, it is stated that the Lamanites hated the Nephites because they felt their ancestors had been wronged by the ancestors of the Nephites (another group of Book of Mormon people who were the descendents of Lehi’s fourth son, Nephi and his followers). These two groups were often engaged in lengthy wars and contentions. In fact, the Book of Alma, which takes up the largest part of the Book of Mormon is almost completely filled with explanations of wars that occurred between the Lamanites and Nephites.
Throughout the Book of Mormon many of the literal Lamanite descendents accepted the gospel of Jesus Christ, became righteous and joined the Nephites. There were also many Nephites who dissented from the gospel, became wicked and joined the Lamanites. This happened so often with such large numbers of people that the terms Lamanite and Nephite no longer represented ancestry and instead represented two separate cultures; the term Nephite came to represent those who followed God’s law and were righteous, and Lamanite was used to describe those who were wicked.
For a short time (about AD 34 to AD 230) after the resurrected Christ visited the Americas (see 3 Nephi 11) the division between Lamanite and Nephite was not used because all the people had become righteous. In 4 Nephi 1:17 we read,
There were no robbers, nor murderers, neither were there Lamanites, nor any manner of -ites; but they were in one, the children of Christ, and heirs to the kingdom of God.
As wickedness slowly came back, the terms were brought back and used again as a way to distinguish between the righteous and the wicked. In 4 Nephi 1:20 it reads,
And he kept it eighty and four years, and there was still peace in the land, save it were a small part of the people who had revolted from the church and taken upon them the name of Lamanites; therefore there began to be Lamanites again in the land.
The true believers began to call themselves Nephites.
Many of the people, including Nephites, became wicked and by AD 400 all of the Nephites were destroyed in numerous wars with the Lamanites.