The text of the book is a transcribed speech which Judith Martin gave to students at a certain Ivy League institution. It covers a short history of official American manners, such as when President Thomas Jefferson tried to apply his democratic ideals by calling all foreign envoys "Mr. Stuart" and the like, as opposed to using titles in official protocol. This idea did not last.
However, there really isn't that much substance in this book that has not been covered in one of Ms. Martin's many other books. Her main idea is that, as a democratic society, social manners should not depend on money or rank, but egalitarianism, where the fair way to decide precedence is by age -- simply for the reason that everyone eventually gets their chance to take precedence, should they live long enough. Still, reading this prompted me to write Ms. Martin to ask her to write a more complete book on the history of American etiquette. I still await that book.
I would recommend buying a different book by Ms. Martin; the wait I had to get this book wasn't worth it.