Prussia’s defeat of Austria in the Seven Weeks’ War in 1866 had confirmed Prussian leadership of the German states and threatened France’s position as the dominant power in Europe. The immediate cause of the Franco-German War, however, was the candidacy of Prince Leopold of Hohenzollern-Sigmaringen (who was related to the Prussian royal house) for the Spanish throne, which had been left vacant when Queen Isabella II had been deposed in 1868. The Prussian chancellor, Otto von Bismarck, and Spain’s de facto leader, Juan Prim, persuaded the reluctant Leopold to accept the Spanish throne in June 1870.
Supreme Power or Authority.
The answer is: He wanted to amass as much land as possible for France.
At that time, Napoleon believe that Acquiring as much land as possible is the key to ensure the French empire's wealth for the following generation.
He see that lands contain a large number of opportunities because lands often contain various type of resources that can be used as materials for products to be sold to other country.
