Swedish pre-history ends around 800 AD, when the Viking Age begins and written sources are available. The Viking Age lasted until the mid-11th century. Scandinavia was formally Christianized by 1100 AD. The period 1050 to 1350—when the Black Death struck Europe—is considered the Older Middle Ages. The Kalmar Union between the Scandinavian countries was established in 1397 and lasted until King Gustav Vasa ended it upon seizing power. The period 1350 to 1523when king Gustav Vasa, who led the unification of Sweden in the Swedish War of Liberation, was crowned – is considered the Younger Middle Ages. During these centuries, Sweden gradually consolidated as a single nation.
Viking Age
Until the 9th century, the Scandinavian people lived in small Germanic kingdoms and chiefdoms known as petty kingdoms. These Scandinavian kingdoms and their royal rulers are mainly known from legends and scattered continental sources as well as from Runestones. The Scandinavian people appeared as a group separate from other Germanic nations, and at this time there was a noticeable increase in war expeditions (Viking raids) on foreign countries, which has given the name Viking Age to this period. At this time the seas were easier to travel than Europe's inland forests, and the wild buffer regions that separated the kingdoms of the time were known as marches.
Voyages to foreign countries
The Swedes took part in many Western raids against England alongside the Danes and Norwegians of which many successfully acquired Danegeld as seen on the England Runestones. The Swedes were also very active traders and raiders in the eastern and southeastern parts of Europe. The large Russian mainland and its many navigable rivers offered good prospects for trading and plundering. These routes brought them into contact with the Byzantine and Muslim empires. The latter led, among other things, to the formation of the Varangian Guard, an elite fighting force made up by Norsemen. The scholarly consensus is that the Rus' people originated in what is currently coastal eastern Sweden around the eighth century and that their name has the same origin as Roslagen in Sweden (with the older name being Roden).
During the 9th century, extensive Scandinavian settlements were made on the east side of the Baltic sea. The Tale of Bygone Years (dated to 1113) tells of how the Varangians arrived in Constantinople, and of pirate expeditions on the Black Sea and the Caspian Sea.
The Varangians accumulated great wealth from their foreign trades. A centre of trade in northern Europe developed on the island of Birka, not far from where Stockholm was later constructed, in mid-latitude Sweden. Birka declined drastically by 960, but archaeological finds indicate it was wealthy in the 9th and 10th centuries. Thousands of graves, coins, jewelry and other luxury items have been found there.
Early rulers
Medieval Danish, Norwegian, Icelandic and Anglo-Saxon sources tell of Migration Age Swedish kings belonging to the Scylfing dynasty, also known as Ynglings. Some sources, such as Íslendingabók, Ynglinga saga and Historia Norwegiæ trace the foundation of the Swedish kingdom back to the last centuries BC. Some of these sources, the Anglo-Saxon Widsith and Beowulf, may date to the 8th century in their present forms, but retain oral traditions that are considerably older. Native Scandinavian sources are generally held to date no earlier than the 9th century in the form of skaldic poetry, such as Ynglingatal. The Scandinavian sources were not put to paper until the 11th century and later.
In a mythological sense, the first king of Sweden is said to have been Odin as the founder of the house of Yngling. (See also List of legendary kings of Sweden.)
The earliest kings whose names appear in different traditions (Beowulf and Ynglingatal) are three kings from the 6th century, starting with Ongentheow or Egil. The first kings attested in a contemporary source are those mentioned in Rimbert's Vita Ansgarii, from the 9th century.
Before the 10th or 11th century, there were many different petty kings, who ruled over different parts of the future Sweden and a lot of fighting and disputes between different tribes, such as the Geats and Swedes, and different sources contradict each other. These contradictions persists up to and after the reign of Eric the Victorious, who ruled around 970–995, but some facts about him can be established. Eric was succeeded by his son King Olof Skötkonung (late 960s), the first Christian king of Sweden, and the first who is known to have ruled over the different tribes. Olof is listed first in medieval Swedish regnal lists, but modern ones usually starts with his father.