This book has been sitting on my shelves for a few years, waiting for the right time. I often try to pick a heavier volume for the Proms season as it offers the opportunity to do more reading while queueing, and it's been good to finish this just before the end of the season.
The book traces the origins of the Hohenzollern state to 1417, when the Burgrave of Nuremberg bought the Electorate of Brandenburg. The first few chapters deal with the precarious state of affairs in the seventeenth century, during the Thirty Years War, when Brandenburg variously tried neutrality and alliances with each side in turn, but was thoroughly trampled in the process. The era of the Great Elector transformed the state, by acquiring sufficient military resources for defence, and also expanding the territory through military and inheritance means, a process furthered a hundred years later by Frederick the Great, someone I would have no difficulty in describing as a liberal authoritarian. There's a lot of material about religion during these times: power struggles principally between Catholics, Lutherans and Calvinists, though Clark also notes with regularity the power blocs and struggles of various local aristocracy and an increasingly centralising government.
The next major upheavals occur with the Napoleonic period, before moving on to the revolutionary year of 1848, and wars leading to German unification in the 1870s. The First World War features only lightly in the book, but more attention is paid to the rise of the Third Reich: Clark goes into some detail on the rise of the Nazis in 1920s and 1930s Germany, noting in particular their relative lack of popularity in Prussia. Nevertheless, and not without historical justification, Prussia was considered a warmongering state and constitutionally abolished by the Allies in 1947.
This is a very thorough book. I felt I learned more about the Holy Roman Empire than I did from Norman Davies' book on Europe. The sections on Frederick the Great and the Third Reich were quite illuminating, but other parts were rather dry, so I think it may be a book that satisfies existing interests more than inspiring new ones.