When and How did the Distinction Between the Geats and the Swedes End?

This is a very difficult question to answer. But to make an attempt, this would be a gradual process, and one needs to be aware that people in general had more than one identity. Religion, county/region, language, laws, monarch, economical status, profession and class were all important in how someone identified, and acted towards other identities.

In general, Sweden centralised into a nation-state later than the other Scandinavian countries, and it can be argued that as late as 1167 when the Eastern Geats elected their own Kings (Kol and Burislev) in opposition to the King elected by the Western Geats and Swedes (Knut Eriksson), enough people considered Sweden as a union of three crowns rather than a unitary Kingdom that they felt comfortable electing King(s) of a single part of it. After Knut Eriksson defeated Kol and Burislev in battles 1169 and 1173, the Kingdom was re-united and never separated again, so I personally tend to use that as the "safe" starting year for Sweden.

However, parts of what is today's eastern part of Geatland, Småland, was not part of the Kingdom of Sweden and was slowly integrated during the 1200s - as late as 1123, the Norwegian King Sigurd made a combined crusade and plundering expedition to re-convert the Smålanders to christianity, since they had reverted to their pagan ways, or at least decided to not tithe anymore.

Law systems and rights seem to have been an important identifier - the oral county laws, decided and enforced at the things started to be written down in the 1200s, but had a long tradition before that. Geats and Swedes had in common that formal nobility was not introduced until the Alnsö law of 1280, by royal decree, and that the peasants had a right to be represented at the things and the estate parliaments that started to to replace them by the 1400s.

The first common law for all of Sweden is compiled sometime in the 1350s as Magnus Eriksson's law to replace the various county laws and create a uniform law system. Before that, the canon church laws had been the same, enforced by the catholic church.

The long civil war that was the Kalmar Union saw the peasants and the nobility rising several times, sometimes with conflicting goals, sometimes with common goals. The peasants, more afraid of going the way of their continental and Danish brethren to become serfs than death itself, usually referred to their "old rights" and " the respect for Swedish law" as reasons for revolting - however, economic hardship due to taxes and salt blockade due to war seem to have been at least as much the reason during the great Engelbrekt rising of 1434. The nobility often made references to treaties and law, but behaved pretty much opportunistic, switching side between the union and independence parties between generations and as expedience ruled.

Despite a growing sense of nationalry under the same crown, the same law and the same monarch and with the creation of a modern state with modern institutions such as tax census, tax collection, a national army (if very small) during the reign of Gustav I 1523-1560, regionalism was still alive and well in Sweden. Småland, always less inclined to be fond of centralised rule revolted on its own and threw out its Danish and Danish-paid bailiffs and governors at the same time as Gustav Eriksson (Vasa) incited Dalarna to join him in a revolt. Likewise the peasants in Uppland had already risen once the men from Dalarna arrived.

Småland would also present one of the greatest challenges to Gustav Eriksson (Vasa)s rule as Gustav I - the Dacke rising, which managed to hold Småland for a year before being crushed by royalist forces.

The border area between Småland and Skåne were the place of well documented peace treaties between the peasants of each region, 1525, 1542, 1563 and 1611 they met, agreed to not partake in any raids or campaigns against each other, co-operate to drive off bandits and the various plundering non-military elements that were part of all armies of that era and warn and even shelter each other in case an army came marching - regardless of whose army it was and where it came from. Clearly the peasants here valued their identity as regional neighbours and their class identity as peasants more than their national identity as Swedes or Danes.

So, to sum things up. A person in the Stockholm area of Sweden in the 1100s would probably identify as christian (as opposed to his pagan forefathers), norse (as opposed to Rus or German), a Swede (as opposed to a Geat, a Jutlander, a Trönd or a Scanian), under the Uppland law (as opposed to people under the Västergötland or Östergötland law), as a self-owning peasant (as opposed to a great man or a tenant peasant) and as a man with rights to be heard by the lawman and his peers at the thing for complaints (as opposed to thralls or foreign serfs).

A person in the 1600s would identify as protestant (as opposed to catholic Germans and orthodox Russians), Swedish (as opposed to Norwegian or Danish), under Swedish law (as opposed to other people in the Swedish Empire, such as Estonians and Latvians, who were under their own laws), as a self-owning peasant (as opposed to a nobleman, a burgher, a priest or a tenant peasant or crofter) and a man with a right to be judged by his peers at the Häradsrätt and to be represented at the estates parliament (as opposed to foreign serfs under the justice of their land owners and peasants with no representation in other countries).

What kind of identity someone would identify with would switch with the circumstances and what they were comparing themselves with. A Geat may call himself a Geat when comparing himself to a Swede, while calling himself Swedish when comparing himself to a Danish man.

The whole issue is a complicated mix of history, culture, language, laws, crowns, nationality and very much a sliding scale, both over time and at any given moment.