Latvia is a country in Northeast Europe bordered by Estonia, Lithuania, Russia and Belarus. Latvia is mostly flat and contains primarily short rivers, with woodlands that cover around half of the country and few rivers that exceed 60 miles. Riga is Latvia's most populated city, as well as its economic and political core. The city's strategic position on the Gulf of Riga, at the mouth of the Daugava river, has traditionally made it an important trading post in northern Europe. Indeed, Riga was a member of the Hanseatic League, a confederation of market towns, in the 13th century. However, Latvia is also surrounded by major powers and is easy to invade. For centuries, Latvia was under the influence or direct control of its neighbors, including German crusaders, the Polish-Lithuanian Commonwealth and the Russian Empire. Latvia briefly became independent after World War I, but was absorbed by the Soviet Union during World War II and did not regain its independence until 1991. Since then, Latvia has sought to integrate with the West. It joined the European Union and NATO in 2004, and the eurozone in 2014. Membership in these organizations forced Latvia to undergo rapid institutional modernization and economic liberalization. Currently, the country's economy relies primarily on exports. Latvia's main geopolitical challenge has traditionally been preventing foreign aggression. In this regard, modern Latvia's primary concern is Russia. Latvia view membership with the European Union and NATO, as well as its ties with the United States, to guard against Russian interference. Still, Latvia imports the majority of its natural gas from Russia, and Russian money has a significant presence in Latvia's banking sector. Moreover, roughly a quarter of Latvia's population speaks Russian, and their status is often a source of friction between Russia and Latvia.