The Franco-Prussian war took place in 1870-71 between the European countries of France and Prussia. Although not well known to the man on the street, it was an important war for European politics, as it resulted in the unification of the German states into the single country of Germany, setting the stage for World War I.
You also may be asking 'Prussia? Where's that?' And you may well, since it doesn't exist any more. Prussia constituted parts of Eastern Germany and Poland, though its influence at the height of its power would stretch into Western Germany, Slovakia, Kaliningrad (now part of Russia), Latvia, Southern Denmark and Lithuania. Prussia is represented by the blue on this map: http://en.wikipedia.org/wiki/File:Map-DR...
Berlin was the capital of the Prussian Empire, and served as the capital of Germany after its unification. After World War I many parts of former Prussia were divided up into newly independent countries. Prussia continued to exist as a state within Germany until after WWII, when the vast state was split up into provinces.
Causes of the War
The causes of the Franco–Prussian War are many, most deeply rooted in the events surrounding the idea of German Unification; uniting all of the German-speaking countries into one empire. In the aftermath of the Austro–Prussian War(1866), Prussia had annexed numerous territories, destabilizing the European balance of power established by the Congress of Vienna in 1815, after the Napoleonic Wars. I know that seems to be a lot of war to keep track of. The main point is, though, that Prussia had gotten very large and powerful, and was still looking for more countries to add to itself.
Of course, Napoleon III of France did not care for that idea one bit. He demanded compensations in Belgium and on the left bank of the Rhine to secure France's strategic position. The Prussian chancellor, Otto von Bismarck, flatly refused. Instead, he looked to annex even more, seeking to incorporate the southern German kingdoms Bavaria, Wurttemberg, Baden and Hesse-Darmstadt, into a unified Prussia-dominated Germany.
In Spain, Queen Isabella II was overthrown. Looking to take over the monarchy was Prince Leopold of Hohenzollern-Sigmaringen, a relative of the king of Prussia, King William I. If this were to occur, then France would be completely surrounded by members of the Hohenzollern dynasty. Bismarck realized that this may be his chance to dispose of France permanently. However, much to the dismay of Bismarck, King William I withdrew his candidacy for Spain, in order to avoid war. France pushed for a formal apology to France from William I. When Bismarck received a telegraph from William I with this request, he altered it to make it look very insulting to the French, hoping this would cause France to declare war. It worked, as France declared war on Prussia on July 19, 1870.
At this time in history, Prussia had the largest military in the world. The French were really no match for the better-trained, better-organized, better-led Prussian army. Additionally, The southern German states honored an old military alliance, and came to the side of the Prussians. The Prussian army marched into Sedan on September 2, 1870 and captured a large French force, including Napoleon III himself. Paris, however, continued to fight for the next four months, until it was captured on January 28, 1871.
A Peace treaty was signed in May that had France pay 5 million francs to Prussia, as well as give up the eastern provinces of Alsace and Lorraine to the German state. Even before this, the southern German states agreed to enter the North German confederation, or the unified northern German states. On January 18, 1871, in the Hall of Mirrors at Versailles, France, Germany officially become unified under the Prussian monarchy and William I was proclaimed the German Emperor (not the Emperor of Germany).