The book is a history of how people thought about strategy, rather than a history of how strategy was applied or what the strategic conditions were. Its very long, and difficult to retain most of it. Its most entertaining in the beginning when the focus is more zany: how chimpenzees fight wars. The strategic considerations in the bible. Was the devil in Paradise Lost Michevalian.
Beyond that, things that I got out of the book were
(1) Jomini was a French rival to Claustowitz who I never heard of (2) A lot of Toltsoy's writing was a rebuke of Claustowitz (3) I liked the lens of Communism as "strategy from below" and their theory of history was transforming society into a battlefield (4) Sociology was initially a reaction to Communism which Weber disliked (5) The strategic idea I liked the best was linear strategies vs strategies by attrition. In a linear strategy a series of steps have to unfold correctly to succeed. vs attritional you have lots of unrelated battles and the cumulative outcome decides what happens