Your challenge, should you choose to accept it, is to obtain a united German state based on the German Confederation by the present day with a POD no earlier than 1850. It should include not just the territory of the Bund but also Prussian lands outside it (Posen and Baltic Prussia), Schleswig, Alsace, and Heligoland.
You are free to make it as centralized or decentralized as you wish (provided it remains an actual country) and assign a dominant role to whichever German state you please. Given the POD limitations you can't use the Spring of Nations.