In developing this book over a period of more than 20 years, I lost track of the tens of thousands of books, articles, and references that contributed to it. On military affairs alone, I read or scanned several thousand articles while contributing 12 of my own. Another problem with references on systems is that most are overwrought with mathematical description and esoteric expressions. The exceptions comprise a comparative handful of general references and these were the most useful. The few listed here were the most helpful to me, exclusive of thousands of forays into the Encyclopaedia Britannica and the Great Books of the Western World set.