The consolidation of Sweden involved an extensive process during which the loosely organized social system consolidated under the power of the king. The actual age of the Swedish kingdom is unknown. Also, for various reasons, scholars differ in defining early Sweden as either a country, state or kingdom.
Unlike the histories of Denmark and Norway, there is no agreement on a reliable date for a unified Sweden. Historians judge differently the sources for the history of Sweden's consolidation. The earliest history blends with Norse mythology. Early primary sources are foreign; secondary sources were written at a later date.
Based on the origins of the name of the kingdom as meaning (Kingdom of the Swedes), some historians have argued that Sweden was unified when the Swedes first solidified their control over the regions they were living in. The earliest date for this is based on a brief section in the Roman historian Tacitus discussing the Suiones tribe. This would imply that a Swedish kingdom would have existed in the first to second centuries AD. However, with the increased rigour of historical method advanced in 20th century historical research, in Sweden as elsewhere, historians such as Curt Weibull and his brother Lauritz maintained that these perspectives have become obsolete. Modern historians noted that a millennium had passed between Tacitus and more in-depth and reliable documented accounts (or notices of contemporary events relating to Sweden by Frankish and German writers) of Swedish history. The work of Birger Nerman (1925), who argued that Sweden held a senior rank among the existing European states at the time represents a nationalist reaction to the academic historiography, with the latter taking a critical or cautious view of the value of old layers of sources of history especially if these documents and traditions are unsupported by any direct traces, any footprint of events and social or political conditions in the archaeological records, buildings, coinage etc. of the age in question.
A common definition of Sweden is that it was formed when the Swedes and Geats were ruled by one king. The names Swedes and Geats are attested in the Old English poems Beowulf (written down in the 11th century) and Widsith (from the 8th century) and building on older legendary and folklore material collected in England. In both poems, an Ongentheow (corresponding to Angantyr in Icelandic sagas) is named as the King of the Swedes, and the Geats are mentioned as a separate people. These names of peoples living in present-day Sweden, the Anglo-Saxon references and now lost tales they were attached to must have travelled across the North Sea. The first time the two peoples are documented to have had a common ruler is during the reign of Olof Skötkonung about AD 1000.
Broadly speaking, Kings of Sweden, and the nobility of the land, have seen Götaland and Svealand as equally important parts of the kingdom at least since the mid-13th century and, in some cases, considerably earlier.
Rather than the unification of tribes under one king, others maintain that the process of consolidation was gradual. Nineteenth-century scholars saw the unification as a result of a series of wars based on evidence from the Norse sagas. For example, according to the Norwegian Historia Norwegiae and the Icelandic historian Snorri Sturlusson, a 7th-century king called Ingjald illråde burnt a number of subordinate kings to death inside his hall, thus abolishing the petty kingdoms in the consolidation of Sweden.
To solve the problem of defining an early history of Sweden that coincides with reliable sources, a group of modern Swedish historians have contended that a real state could only exist, in the Middle Ages, if it had the backing of Christianity and the clergy. The same connection between Christianity and consolidation is used in other countries where written sources are less scarce, such as England or Harald Bluetooth's Denmark. The definition is based on the fact that English and German priests would have brought organizational and administrative skills needed for statehood (including by local rulers). The process of consolidation would have required this important ideological shift. While an Iron Age Germanic king would claim the elective support of his people, and the Norse gods, a crowned Christian king would claim that his rule was divinely inspired. According to this definition the unification should be completed in 1210 when Erik Knutsson was crowned by the church, or perhaps in 1247 when the last separatist rising was defeated at Sparrsätra. A major problem sometimes pointed out with that view is that it entails circular proof: we know next to nothing about how the authority of the ruler was envisaged in heathen times, while we know some more of the Christian ideology of kingship, and obviously the Christian kingdom would underline the break with the pagan past, but this does not really allow the conclusion that there could have been no fixed and religiously connected ideas of the authority of the ruler in pre-Christian times. Moreover, we have no solid testimonies fixing it as a fact that the king residing in Central Sweden (the lake Mälar/Östergötland area) was actually recognized as king in all of the area that was called Sweden by the 13th century, when the mist really clears. There may have existed local kings in Western Sweden, even though their names have not been preserved.
That Sweden went through a process of consolidation in the early Middle Ages is generally agreed upon, but royal authority was often contested all through the Middle Ages, and sometimes barely even exercised. Gustaf Vasa (1523–60) determinedly strengthened the central power and mightily increased the authority and resources of the crown, and his reign marked the beginning of the early modern Swedish state. The full and complete process of territorial consolidation behind natural borders (the Baltic Sea, the North Sea, and woodland and mountains separating the country from Norway) reached a decisive point only in the 17th century with the treaty of Roskilde (1658); however, at the time, the idea of "natural borders" or even territorial continuity was not seen as essential to a state. The current borders of Sweden were not settled until 1809 with the loss of Finland to Russia in the Finnish War. With the loss of Finland, which was seen as a national disaster by contemporary Swedes and certainly redefined the nation, and a few years later of its last German possessions (acquired in the Peace of Westphalia), the country had reached the shape it still has, and also entered a period of peace in relation to its neighbours.
- Hadenius, S; Nilsson, T and Åselius, G. (1996:13):
"Hur och när det svenska riket uppstod vet vi inte. Först under 1100-talet börjar skriftliga dokument produceras i Sverige i någon större omfattning [...]" "How and when the Swedish kingdom appeared is not known. It is not until the 12th century that written documents begin to be produced in Sweden in any larger extent [...]"
- "Suionum hinc civitates", Germania 44, 45
- Nordic historiography in the 20th century, 2000, ISBN 82-550-1057-2
- Nationalencyclopedin online (in Swedish), retrieved 2016-01-11:"Olof Skötkonung brukar anföras som den förste kung som med säkerhet kan sägas ha regerat över såväl Svealand som Götaland.", "Olof Skötkonung is usually given as the first king that we know for sure ruled over both Svealand and Götaland".
- Maja Hagerman (2004). Spåren av kungens män: om när Sverige blev ett kristet rike i skiftet mellan vikingatid och medeltid (in Swedish). Pan. ISBN 978-91-7263-558-6.
- Dick Harrison (2002). Jarlens sekel (in Swedish). Ordfront Förlag. ISBN 978-91-7441-359-5.
- Stig Hadenius; Torbjörn Nilsson; Gunnar Åselius (1996). Sveriges historia: vad varje svensk bör veta (in Swedish). Bonnier Alba. ISBN 978-91-34-51784-4.
- Jan Arvid Hellström (1996). Vägar till Sveriges kristnande (in Swedish). Atlantis. ISBN 978-91-7486-233-1.
- Henrik Lindström; Fredrik Lindström (1 January 2006). Svitjods undergång och Sveriges födelse (in Swedish). Albert Bonniers Förlag.
- Birger Nerman (1925). Det Svenska Rikets Uppkomst (in Swedish). Generalstab.
- P. H. Sawyer (1989). The Making of Sweden. Viktoria Bokförlag. ISBN 978-91-86708-08-5.