How To Plan A Crusade. Christopher Tyerman. Penguin Books (2015)

A hugely engaging and enjoyable book about the work that was needed to be done in order to get the various crusades launched and maintained. The crusades have developed impressive layers of mythology around every aspect of their intentions, operations, importance and historical impact. The fact that they were overtly a religious enterprises launched from Europe to protect, recover and maintain Christian sites from the grasp of Islamic rulers they have always been deeply convenient fodder for the enduring "clash of cultures" outbursts.
Christopher Tyreman gracefully sidesteps most of this historical quicksand by concentrating on a less attended to aspect of the crusades. The fact that they were enormous examples of international military, diplomatic and political cooperation that needed to be thoughtfully and systematically organised to take place at all. The particular crusade myth that Christopher Tyeman wishes to remove is the idea that they were spontaneous events arising off a popular religious wave that swept up populations and sent them to unplanned war. Getting large numbers of troops to any location requires concerted planning, getting troops from different countries to a distant location with all of the logistics and supply problems that incurs at any time in history, required a very significant level of coordinated international planning. It is the components of this international, coordinated planning that is examined with telling detail and engaging critical analysis in this book.
The book examines the planning for the crusades under 5 headings, Justification, Propaganda,Recruitment, Finance and Logistics. Each is traced as they developed and responded to the results of previous crusades. The enormous energy and demands that establishing and launching a crusade required created dynamic changes that had long term implications far beyond the crusades themselves.
One of the most engaging aspects to this book is that Christopher Tyerman is actively pursuing an argument with the reader. The purpose of the book is to persuade, backed by a wealth of historical evidence and  analysis, the reader that the crusades and their context are considerably more grounded in rational investigation and considered practical planning than religious mania. The book has to stand or fall on the extent to which the argument is successful both in the way it is presented and the extent to which it convinces the reader.
I think that Christopher Tyerman has succeeded brilliantly on both counts, the organisation of the book is superb and the argument is clearly delivered and compelling. The single most important thing that Christopher Tyerman does in the book is to place the efforts so completely within the context of the times they took place, he shows very clearly how the justification and the propaganda were intrinsic to the social and political structures of the Middle Ages, and how both were considerably more fluid than is often assumed.
Personally I found the sections on finance and logistics to be the most engaging as I have a deep professional interest in both and to see how extremely familiar problems were solved with strikingly similar processes to today was intriguing.
This is a great book, it wears it very considerable learning lightly, the relevant details are provided in a clear and thoughtful fashion and the central argument is made isn a compelling fashion. It is a pleasure to read and think about.