Sweden (officially the Kingdom of Sweden), is a Scandinavian country in Northern Europe. Sweden borders Norway and Finland, and is connected to Denmark by a bridge-tunnel across the Öresund. At 450,295 square kilometres, Sweden is the third-largest country in the European Union by area, with a total population of about 9.7 million. Sweden has a low population density of 21 inhabitants per square kilometre, with the population mostly concentrated in the southern half of the country. About 85% of the population lives in urban areas. Southern Sweden is predominantly agricultural, while the north is heavily forested. Sweden is part of the collective geographical group of nations Fennoscandia.
Germanic peoples have inhabited Sweden since prehistoric times, emerging into history as the Geats/Götar and Swedes/Svear and contributing to the sea peoples known as the Vikings.
Swedish pre-history ends around 800 CE, when the Viking Age begins and written sources are available. The Viking Age lasted until the mid-11th century, when the Christianization of Scandinavia was largely completed. The period 1050 to 1350 - when the Black Death struck Europe - is considered the Older Middle Ages. The period 1350 to 1523 - when king Gustav Vasa, who led the unification of Sweden, was crowned - is considered the Younger Middle Ages.
During this period, Sweden was gradually consolidated as a single nation. Scandinavia was formally Christianized by AD 1100. The Kalmar Union between the Scandinavian countries was established in 1397 and lasted until Gustav Vasa ended it upon seizing power.
In the 17th century, the country expanded its territories to form the Swedish Empire. The empire grew to be one of the great powers of Europe in the 17th and early 18th centuries. Most of the conquered territories outside the Scandinavian Peninsula were lost during the 18th and 19th centuries. The eastern half of Sweden, present-day Finland, was lost to Russia in 1809. The last war in which Sweden was directly involved was in 1814, when Sweden by military means forced Norway into a personal union. Since then, Sweden has been at peace, remaining a largely neutral nation. The union with Norway was peacefully dissolved in 1905. Sweden played a role in humanitarian efforts during World Wars I and II, taking in refugees from German-occupied Europe. With the ending of the Cold War, Sweden joined the European Union, but declined NATO membership.