The Kingdom of Prussia (German: Königreich Preußen) was a German kingdom that constituted the state of Prussia between 1701 and 1918 and included parts of present-day Germany, Poland, Russia, Lithuania, Denmark, Belgium and the Czech Republic. It was the driving force behind the unification of Germany in 1871, and was the leading state of the German Empire until its dissolution in 1918. Although it took its name from the region called Prussia, it was based in the Brandenburg, where its capital was Berlin.
The unification of Germany into a politically and administratively integrated nation state officially occurred on 18 January 1871 at the Versailles Palace in the Hall of Mirrors in France. Princes of the German states gathered there to proclaim Wilhelm I of Prussia as German Emperor after the French capitulation in the Franco-Prussian War. Unofficially, the de facto transition of most of the German-speaking populations into a federated organization of states had been developing for some time through alliances formal and informal between princely rulers — but in fits and starts, as self-interests of parties hampered the process over nearly a century of aristocratic experimentation from the dissolution of the Holy Roman Empire (1806) and the subsequent rise of nationalism over the span of the Napoleonic Wars era.