I'm not answering the question, but you're misreading that section. The actual quote is not from the author, but from Frederick the Great (chapter 2, page 33):

The lands of the Elector, Frederick the Great wrote over a century and a half later, ‘were desolated during the Thirty Years’ War, whose deadly imprint was so profound that its traces can still be discerned as I write’.

And the quote is from: Frederick II, Mémoires pour servir à l’Histoire de la Maison de Brandebourg (2 vols., London, 1767), vol. 1, p. 51.

Forgive me, but the question seems incomplete: when in the book the author says that there was "physical legacy", to what year does he refer ? 1947 ?