The correct answer is A) Prussian military power.
A MAJOR factor in bringing about the unification of Germany was Prussian military power.
William 1 of Prussia was proclaimed German emperor on January 18, 1871, as a result of the German unification. Germany started its political and administrative life as a national state, as was the decision of the Princes of the German territories agreed at the end of the Franco-Prussian War. Yes, Otto von Bismarck and the Prussian Army played a big role in the unification.