More than 60% of the History of the Church was compiled after the death of Joseph Smith, and several passages were altered from William Clayton’s diaries to make them appear to be the writings of Joseph Smith; an easy sign of plagiarism.
“For instance, under the date of May 1, 1843, Clayton recorded this statement concerning the Kinderhook plates in his diary:
“Pres[ident] J.[oseph Smith] has translated a portion and says they contain the history of the person with whom they were found & he was a descendant of Ham…”
In the History of the Church this has been falsified to make it appear that Joseph Smith was the author:
“I have translated a portion of them, and find they contain the history of the person with whom they were found. He was a descendant of Ham…”
~JS History of the Church 5:372~
~Tanner, Clayton’s Secret Writings Uncovered, Introduction; 1982~