A republic in central Europe; a federal parliamentary republic of sixteen states (Bundesländer). The capital and largest city is Berlin. Germany is a member of the United Nations, NATO, the G8, the G4 nations, and signed the Kyoto protocol. It is the world's third largest economy by nominal GDP, the largest exporter of goods, ranked sixth in military expenditure, and is home to the third-highest number of international migrants. Germany has developed a high standard of living and established a comprehensive system of social security. It holds a key position in European affairs and is recognized as a scientific and technological leader in several fields; split into East German and West Germany after World War II and reunited in 1990.