Harry Cook has written a real gem of karate history, "Shotokan Karate - A Precise History", distributed by Tsunami/Dragon Times.
Outside of being the most indepth analysis of the development of Shotokan, it also provides a template of developing karate in Japan that you will see played itself again many times as the art(s) spread to other cultures and had to deal with the same issues.
The book is filled with detail and is well written. It is bound to become one of the classics in Martial Literary history.
Bushi No Te Isshinryu