D. The division of the German people into many states.
Explanation:
In the mid-1800s the German territory we know today, was composed of 39 independent states unified only by language and geography. This was a major obstacle to the German unification (1850-1871) led by the Prussian leader Otto von Bismarck, as well as the competition of Prussia with Austria, the difference of religions and the difference of political views.
