Berlin is the capital city and one of sixteen states of Germany. With a population of 3.4 million within its city limits, Berlin is the country's largest city. It is the second most populous city and the eighth most populous urban area in the European Union. Located in northeastern Germany, it is the center of the Berlin-Brandenburg metropolitan area, comprising 5 million people from over 190 nations. First documented in the thirteenth century, Berlin was successively the capital of the Kingdom of Prussia (1701-1918), the German Empire (1871-1918), the Weimar Republic (1919-1933) and the Third Reich (1933-1945). After World War II, the city was divided; East Berlin became the capital of East Germany while West Berlin became a Western exclave, surrounded by the Berlin Wall from 1961-1989. Following German reunification in 1990, the city regained its status as the capital of all Germany. Berlin is a major center of culture, politics, media, and science in Europe. Its economy is primarily based on the service sector, encompassing a diverse range of creative industries, media corporations, environmental services, congress and convention venues. The city serves as a continental hub for air and rail transport, and is one of the most visited tourist destination in the EU. Other industries include traffic engineering, optoelectronics, information technology, vehicle manufacturing, biomedical engineering, and biotechnology.