Correct option is D
Information Booster:
After the Austro-Prussian War of 1866, Austria was excluded from German affairs.
Otto von Bismarck, the Prussian Chancellor, formed the North German Confederation as a step toward German unification.
It was officially established in 1867 and served as a federation of 22 northern German states under Prussian leadership.
This confederation was a precursor to the German Empire, which was proclaimed in 1871.