Geopolitik is the branch of uniquely German geostrategy. It developed as a distinct strain of thought after Otto von Bismarck's unification of the German states but began its development in earnest only under Emperor Wilhelm II. Central concepts concerning the German race, and regarding economic space, demonstrate continuity from the German Imperial time up through Adolf Hitler's Third Reich. However, Imperial geostrategist, German geopoliticians, and Nazi strategists did not have extensive contacts with one another, suggesting that German geopolitik was not copied or passed on to successive generations, but perhaps reflected the more permanent aspects of German geography, political geography, and cultural geography.