As Europe's largest economy and second most populous nation (after Russia), Germany is a key member of the continent's economic, political, and defense organizations. European power struggles immersed Germany in two devastating World Wars in the first half of the 20th century and left the country occupied by the victorious Allied powers of the US, UK, France, and the Soviet Union in 1945. With the advent of the Cold War, two German states were formed in 1949: the western Federal Republic of Germany (FRG) and the eastern German Democratic Republic (GDR). The collapse of the USSR and the end of the Cold War allowed for German unification in 1990. French-German cooperation in the 1990s was central to European economic integration, and in January 1999 Germany and 10 other EU countries introduced a common European exchange currency, the euro. Germany is the fourth-largest economy in the world. More than in most other advanced economies, manufacturing and related services are still the core of the German economy. The country also is one of the most technologically advanced producers of steel, cement, chemicals, machinery, vehicles, electronics, and shipbuilding.