In the second half of the 19th Century, Prussia led and controlled the unification process of the German territories. The ascension of a new great power in the centre of the Continent alerted the French who feared that a unified Germany would endanger the geopolitical equilibrium established in 1815 at the Congress of Vienna. The Franco-Prussian War, a war in which France was defeated, developed against this background. Bismarck opposed the annexation One of the most important clauses of the Frankfurt Peace Treaty signed in May 1871 was the German annexation of certain territories from Alsace – Lorraine. This annexation was perceived as a punitive clause against the warmongering French, however, it caused a stir in Germany as well. Chancellor Bismarck was opposed to the idea, because he realized that the annexation of the French territories would lead to a permanent source of conflict between France and the new German State by producing a strong revisionist movement. On the other hand, Kaiser Wilhelm I supported the Prussian Army who was of the opinion (especially Helmuth von Moltke) that spreading the German borders further west was very necessary. The demographic argument accounted publicly for the annexation: in Alsace – Lorraine the large majority of people spoke German dialects. More important, however, was the military aspect: should the German frontier be extended west, the Kaiserreich would have the strategic upperhand. The Germans would gain control of the Metz fortifications as well as over the iron ores in the region which were essential for the military industry. The domestic policy of the German Empire played a very important part in this decision. Although it was effectively led by Prussia (the Prussian King was the heir of the Imperial Crown and the Prussian prime minister became the Chancellor), the new Empire was nevertheless a decentralized str