Making Prussians, Raising Germans is a great book about the history of German identity A recent post also listed Fatherlands: State-building and Nationhood in 19th Century Germany as an essential read by University of Wisconsin in understanding Modern German history and I’m currently looking for a copy so I haven’t had a chance to read it

I’m no expert on the topic, and would love to see any other suggestions

Edit: This is the full list I was referring to https://history.wiscweb.wisc.edu/wp-content/uploads/sites/202/2017/05/prelim_moderngermany_guenoun.pdf ...In case I missed something that may peak your interest