As a book for the general public, it followed the common practice of not citing sources.
"Then why don't you cite more primary sources in your book?"
I will cite sources and would encourage you to do your own research.
But readers who want to know more will have to rely on the many sources cited in the book.
Good effort, I read with interest, however you really need to cite sources of factual information to back up your opinion.
There is no word minimum or maximum, and students are expected to cite sources.
Citing sources will help increase the credibility of the information in your research essay.
They may not want you to cite such sources, unless your paper includes a direct quote from one.
Notes at the end seem exactly right, citing sources, not too recondite.
However, Harrison has cited other sources of inspiration to the contrary.