Berlin is the capital city of Germany and one of the 16 states of Germany. With a population of 3.5 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union. Located in northeastern Germany on the River Spree, it is the center of the Berlin-Brandenburg Metropolitan Region, which has about 4.5 million residents from over 180 nations. Due to its location in the European Plain, Berlin is influenced by a temperate seasonal climate. Around one third of the city's area is composed of forests, parks, gardens, rivers and lakes.First documented in the 13th century, Berlin became the capital of the Margraviate of Brandenburg (1417), the Kingdom of Prussia (1701–1918), the German Empire (1871–1918), the Weimar Republic (1919–33) and the Third Reich (1933–45). Berlin in the 1920s was the third largest municipality in the world. After World War II, the city was divided; East Berlin became the capital of East Germany while West Berlin became a de facto West German exclave, surrounded by the Berlin Wall (1961–1989). Following German reunification in 1990, the city was once more designated as the capital of all Germany, hosting 158 foreign embassies.