Obviously, a non-fiction book about history will be taken by historians more seriously if there are footnotes (or endnotes) leading to primarily primary sources of documents. I would, of course, like historians to take my work that I just started seriously, but also like it to appeal to "normal" readers as well. The subject of my book about the influence of railways on military history is so broad and covers such a large time period, that I'm afraid I can only get so many primary sources (esp. considering that much of the book will be countries other than in N. America). So, I'll be citing perhaps just as many secondary sources (other books) or perhaps more than primary sources. Is doing what I'm doing frowned upon these days? Any advice? This is my first non-fiction book, btw. Thanks!