Mormon leaders made a mistake

Is it LDS belief that Native Americans descended from Israelites?Some members also explain that Joseph falsely believed that Native Americans were descended from Lehi, and so when he wrote the Doctrine and Covenants, that was how he chose to describe them: as Lamanites.

If true, this raises the uncomfortable realization that Joseph was factually wrong about a fairly important piece of the religion he was preaching, and that his incorrect personal opinions were able to make their way into official doctrine. This leaves open the question of what else he might have gotten wrong.

Brigham Young also made this mistake when he said:

You may inquire of the intelligent of the world whether they can tell why the aborigines of this country are dark, loathsome, ignorant, and sunken into the depths of degradation ...When the Lord has a people, he makes covenants with them and gives unto them promises: then, if they transgress his law, change his ordinances, and break his covenants he has made with them, he will put a mark upon them, as in the case of the Lamanites and other portions of the house of Israel; but by-and-by they will become a white and delightsome people. (Journal of Discourses 7:336)
Spencer W. Kimball believed Brigham Young's prophecy was being fulfilled. In 1960, he said that the Native Americans

"...are fast becoming a white and delightsome people.... The [Indian] children in the home placement program in Utah are often lighter than their brothers and sisters in the hogans on the reservation" (Improvement Era, December 1960, pp. 922-3).
In the conference talk "Of Royal Blood," Kimball further says:

With pride I tell those who come to my office that a Lamanite is a descendant of one Lehi who left Jerusalem six hundred years before Christ and with his family crossed the mighty deep and landed in America. And Lehi and his family became the ancestors of all of the Indian and Mestizo tribes in North and South and Central America and in the islands of the sea, for in the middle of their history there were those who left America in ships of their making and went to the islands of the sea.

"The term Lamanite includes all Indians and Indian mixtures, such as the Polynesians, the Guatemalans, the Peruvians, as well as the Sioux, the Apache, the Mohawk, the Navajo, and others. It is a large group of great people." (Spencer W. Kimball, "Of Royal Blood," Ensign, July 1971, p. 7).
The Book of Mormon, the Doctrine and Covenants, and multiple church leaders beginning from Joseph Smith, all seem to tell a single coherent and consistent story: Modern Native Americans are the direct descendants of Lehi and his family, Israelites, from 600 B.C.Comment:  For more on the subject, see The Indian-Mormon Connection and Mormons Modify Indian Origin.

Below:  "Joseph was instructed by the Lord to preach to the Lamanites who were not really Lamanites."