In the 1860s, the Chancellor of Prussia and master diplomat Otto Von Bismarck provoked short wars with Austria and Denmark in order bind the lesser northern German states to Prussia instead of its rival Austria as the leader of the German people. In July 1870, he engineered a deliberate insult to France, knowing that the proud French would declare war. This war would force the remaining southern German states, such as Bavaria, Hesse, Baden, and Wuertemburg, to honor their treaty obligations and go to war against France under Prussian leadership. A successful conclusion of the war would be the perfect opportunity to unite the German states into an empire under the Prussian King Wilhelm I. On 20 July 1870, Napoleon III, Emperor of France declared War on Prussia, and the German states dutifully declared war on France in turn, just as Bismarck expected.
Bismarck made sure the deck was stacked against the French from the very beginning. Not only did the Germans raise twice as many troops, but they also did it twice as fast due to the efficiency, organization, and planning of Helmuth Von Moltke’s (the Elder) superior General Staff. Von Moltke expanded the concept of mission tactics that placed great faith in junior leaders accomplishing their missions without the pain of micromanagement, and German units consistently out fought and out maneuvered larger French formations. The French relied on a 60 year old Napoleonic reputation for fighting prowess, so inevitably they were outclassed in almost all respects. Over the next seven months the Germans kicked the shit out of the French. They trapped most of the French army in Metz in September, captured Emperor Napoleon III at Sedan in October, and occupied Paris in January. In the jubilation of victory, Bismarck wasted no time and convinced the separate German states to willingly unite with Prussia. King Wilhelm I of Prussia was crowned Emperor Wilhelm I of Germany in the Versailles Palace on 18 January 1871.
The German Empire, or Second Reich (Charlemagne’s was the First Reich) completely upset the balance of power in Europe that had generally kept the peace since Napoleon’s fall in 1815. This led directly to the First World War. (Which of course would lead directly to Hitler’s Third Reich and the Second World War.)