The Birth of Territory is reviewed in Law, Culture and the Humanities by Thanos Zartaloudis (requires subscription). It’s a generous summary of the book and says a few things about the legal aspects of the argument.
To the legal audience the numerous references and remarks on the role of law in the eventual conception of territory (and sovereignty), as well as the explanatory note on the tension and co-existence of, for instance, civil and canon law, would certainly be a useful entry point into the book for students and scholars. The book is, further, a welcome call for continuous exploration of the lines of questioning that are offered in a historically sensitive map of territory and of its relation to law and spatial strategies of power.
You can read more about this book, with links to all the reviews I know of, on this page.