The very short and constricted answer is that a German state came into formal existence in 1871 with the unification of the various German principalities, kingdoms, free cities, and duchies under the leadership of Prussia. This meant that after 1871, a resident of this new state entity could say they were German and were thus a legal citizen of Germany, much like a counterpart from the US or France.

Prior to 1871, the situation is a lot more messy. Nineteenth-century advances in education, literacy, and industry created a more homogenized German culture and more closely knit various parts of Central Europe together. But, while there was a strong sense of Germanic culture and language that transected internal regional boundaries, there was no overarching political unity to Germany. The small German states like Bavaria or Württemberg were fully sovereign state entities with their own heads of state, legal systems, armies, ambassadors, etc. The existence of these small independent states fostered a strong regional tone to German national identity. The Prussian-led state entity of 1871 was nominally a federal government and the various monarchs of what historians sometimes call "Third Germany" (i.e. Germans not Prussian or Austrian) remained the heads of state of the new federal states (Bundesstaaten).

This complicated political development contributed to a national identity that often is very closely connected to local identity. Even though most Germans have consistently preferred to live in and under a single unitary state, German nationalism often has a pronounced local tinge to it.