The emergence of Prussia as the leading German power and the increasing unification of the German states were viewed with apprehension by Napoleon III after the Prussian victory in the Austro-Prussian War of 1866. Bismarck, at the same time, deliberately encouraged the growing rift between Prussia and France in order to bring the states of S Germany into a national union. He made sure of Russian and Italian neutrality and counted—correctly—on British neutrality. War preparations were pushed on both sides, with remarkable inefficiency in France and with astounding thoroughness in Prussia.
The immediate pretext for war presented itself when the throne of Spain was offered to a prince of the house of Hohenzollern-Sigmaringen, a branch of the ruling house of Prussia. The offer, at first accepted on Bismarck's advice, was rejected (July 12) after a strong French protest. But the aggressive French foreign minister, the duc de Gramont, insisted on further Prussian assurances, which King William I of Prussia (later Emperor William I) refused. Bismarck, by publishing the famous Ems dispatch, inflamed French feeling, and on July 19, France declared war.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.