[[Image:Scandinavia-12th century.png|right|thumb|Approximate borders of "Sweden" in the 12th century. Blue and yellow represents the Geats and Suiones tribes; their unification represents one commonly held view of the consolidation into Sweden. Unlike Norway and Denmark, there is no specific time that is generally agreed on concerning when Sweden can be called unified, i.e. that a single king controls the principal parts of Sweden (in principle Uppland, Westrogothia, and Ostrogothia). A common approach attributes this role to those kings who can be proven to have been kings of both Svealand and Götaland in the 12th century, in effect unifying them into a state covering both the east and west coast.
The process was however gradual. 19th century scholars saw the unification as a result of wars, and used evidence from Icelandic sagas to support their speculations. For example, a 7th century king called Ingjald illråde ("ill-ruler") was supposed to have burnt a number of subordinate kings to death inside his hall, resulting in the abolishment of the petty kingdoms. Today, scholars emphasize the importance of Christianity for the emergence of a state in the modern (i.e. medieval) sense. English and priests brought organizational and administrative skills, but more fundamentally, people (including local rulers) got used to the abstract concept of a state, which required an important ideological shift. While a Viking-age king would be just the warlord with the strongest alliance of petty lords, a crowned Christian king could claim that his rule was divinely inspired. The connection between Christianity and consolidation is very clear in other countries where written sources are less scarce, such as England or Harald Bluetooth's Denmark.
In both Medieval Icelandic sources and in contemporary Swedish sources, Sweden and Götaland were two separate nations. In Sögubrot af Nokkrum for instance, Kolmården between Svealand and Ostrogothia is described as the border between Sweden and Ostrogothia (...Kolmerkr, er skilr Svíþjóð ok Eystra-Gautland...), and in Hervarar saga, king Ingold I rides from Westrogothia to Sweden through Smalandia and Ostrogothia: Ingi konungr fór með hirð sína ok sveit nokkura ok hafði lítinn her. Hann reið austr um Smáland ok í eystra Gautland ok svá í Svíþjóð. The lord Bo Jonsson Grip was probably the one who was best acquainted with the geography of the Swedish kingdom since he owned more than half of it. In 1384, he stated in his testament that the kingdom consisted of Swerige (Sweden, i.e. Svealand), Österland (i.e. Finland) and Göthaland (i.e. Götaland).
Since there are several perspectives on what constitutes Sweden, anyone wanting to establish the date for the unification/beginning/birth of Sweden has to define what they mean by "Sweden" and how they delimit the stages in the evolution of a nation, a country or a state.
What is generally agreed on is that Sweden went through a process of consolidation in the early Middle Ages. The current borders of Sweden, however, not laid until in the 17th century, with the treaty of Roskilde and the treaty of Brömsebro, annexing all the present territories.
- Peter Sawyer (1989). The Making of Sweden.
- Maja Hagerman (1996). Spåren av kungens män. (In Swedish).
- Dick Harrison (2002). Jarlens sekel. (In Swedish).
- Jan Arvid Hellström (1996). Vägar till Sveriges kristnande. (In Swedish).