The German Wars Of Unification

Due to a federal execution Prussia and Austria were at war in 1864 against Denmark over Schleswig-Holstein side by side, and they won.  
Thus they got into a dispute over Schleswig-Holstein in 1866 and this finally solved in the war between Austria and Prussia . Prussia fought with Italy, the associations of some southern German states, against Austria and won again. In the end the German Confederation was lost, so the North German Confederation was established under Prussian leadership.
Prussia and France began to dispute in 1870 to the Spanish throne. France called for a waiver of Prussia, but Wilhelm I rejected this in a telegram, called the Emser Depesche, to the former Ambassador in Paris, Otto von Bismarck. After Bismarck had reduced the telegram and let newspapers publishing it, France declaredwar on Prussia and Prussia won again.
Before that war, the southern German states joined Prussia, because they feared a French attack. Bismarck took advantage of this opportunity to advance the crowning of a prussian king to the emperor of Germany and incorporating the southern German states into a united kingdom.
These three wars, in the years 1864-1871 are known as the German wars of unification.