It is most likely that the first migrations to Sweden occurred about 12,000 B.C. when tribes of reindeer hunters followed the herds from the Continent to Sweden. The Sviones (Swedes) are mentioned by Tacitus ( A.D. 98); this indicates that trade links between the Roman Empire and Scandinavia existed. During the Iron Age (500 B.C. - A.D. 1050) the Lake Mälaren valley, in central Sweden, became an influential area, with the Svea tribe in the leading position. The Vikings (c. A.D. 800-1050) were traders who made voyages to many of the Christian countries of Europe. Many of them stayed in countries such as France, England, and Scotland. Many geographical names in these countries are of Scandinavian origin. The Vikings controlled several trade routes in contemporary eastern Russia, but from the tenth century they began to lose their foothold in this market. During the period of 800-1050 Sweden was frequently visited by Christian missionaries from France, Norway, Denmark, Russia, and Germany. Toward the end of the tenth century, Sweden had been transformed into a Christian kingdom and a united state. In the thirteenth-century Swedish "crusades," Sweden—with the double goal of Christianization and conquest—moved against Finland and the eastern Baltic coast. By the mid-thirteenth century, several Hansa merchants were established in Sweden, and an increase in trade with the Hansa cities followed. German involvement in Scandinavia led to the unification of Scandinavian countries in 1397 under the Kalmar Union; this lasted until 1448. In the following period Sweden was involved in wars with Finland and crushed a Danish attempt to recreate a union. During the seventeenth century Sweden constituted a major power consisting of present-day Sweden, Finland, Ingermanland, Estonia, Latvia, and smaller areas in northern Germany. The country was involved in war for over a hundred years, and Swedish soldiers were in Germany, Czechoslovakia, Russia, and the Baltic States. After 1721 all overseas Swedish provinces were lost with the exception of Finland and Pomerania. In the beginning of the nineteenth century, Sweden became involved in new wars with Denmark and Russia, and Finland was lost to Russia in 1809. This political border was drawn right through a former Culturally homogeneous area—Tornedalen—and thus Sweden obtained a Finnish-speaking minority at the border with Finland. From 1814 to 1905 Sweden was unified with Norway. During World War II, from which Sweden was spared, thousands of refugees came to Sweden, mainly from Denmark, Norway, and Finland but also from Estonia, Latvia, and Lithuania. Before this time Sweden was unusually homogeneous in language and ethnic stock, although it had had an immigration of Germans, Walloons, Dutch, and Scots from the Middle Ages on. But since World War II Sweden has had a net immigration of about 600,000 people, primarily from the European continent but also from Latin America, Asia, and the Middle Eastern countries.
Today there are representatives of 166 different nations living in Sweden. The number of ethnic groups is even higher. There is also a Swedish minority in North America. During the nineteenth century, over a million Swedes emigrated Because of difficult living conditions.