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 and is the second most populous city proper and the ninth 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 4½ 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 was the capital of 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 became divided into East Berlin—the capital of East Germany—and West Berlin, a West German exclave surrounded by the Berlin Wall from 1961–89. Following German reunification in 1990, the city regained its status as the capital of Germany, hosting 147 foreign embassies. Berlin is a world city of culture, politics, media, and science. Its economy is primarily based on the service sector, encompassing a diverse range of creative industries, media corporations, and convention venues. Berlin also serves as a continental hub for air and rail transport, and is a popular tourist destination. Significant industries include IT, pharmaceuticals, biomedical engineering, biotechnology, electronics, traffic engineering, and renewable energy. Berlin is home to renowned universities, research institutes, orchestras, museums, and celebrities, as well as host of many sporting events. Its urban settings and historical legacy have made it a popular location for international film productions. The city is well known for its festivals, diverse architecture, nightlife, contemporary arts, public transportation networks and a high quality of living.