I've given this work 4 stars with a few reservations.
On the plus side, it is a well-written, expertly researched masterpiece of modern history in a classic style (that is to say, it's honestly intellectual, scientifically rigorous and lacking in patronising gimmickery - hooray).
And the story of Prussia is very well told, in a weave that includes rulers, soldiers, politicians, philosophers, scientists, churchmen, and even the ordinary citizen, in buckets.
It is enormously informative as a result, and left me better educated, which should be the point, but...
Well, it's about those bizarre gaps that have irritated at least one other reviewer.
The first one occurs right at the start, when the author asks how it was that Prussia came to be at all, all things considered. It's a good question, and Mr Clark properly weighs some of the considerations. Then he forgets all about it, and starts his narrative proper with a fait accompli. Bizarre.
There is at least one other example of this in the text, before reaching the 20th Century and the rather odd non-mention of the Great War, although the author has by this time already skimmed over several important military events, like the Franco-Prussian War (believe it or not). It's rather as if the book is running out of steam.
Yet, I can understand that Mr Clark might be trying to concentrate exclusively on Prussian history - perhaps German Imperial history is not so important to him, although Bismark nevertheless IS, while William II is not. Nor is the Weimar Republic, nor Hitler, nor the Federal German Republic, other than in terms of a few reflections and musings.
SO you'll need to take this work as a very particular spotlamp, and have your hands on some other works to fill in the shadows (Massie's Dreadnought, for example).