Second Swedish Crusade

The Second Swedish Crusade was a Swedish military expedition to areas in present-day Finland by Birger Jarl in the 13th century. As a result of the crusade, Finland became part of Sweden for the next 550 years.

Year of the crusade
According to Eric's Chronicle from ca. 1320-1340, the crusade took place between Birger Jarl getting elevated to the position of jarl in 1248 and the death of King Eric XI of Sweden in 1250. The so-called "Detmar Chronicle" of Lübeck from around 1340 confirms the expedition with a short note that Birger jarl submitted Finland under Swedish rule. From other sources, Birger jarl is known to have been absent from Sweden in winter 1249-50. Later on, the conquest of Finland was redated to 1150s by the official Swedish legends, crediting the national saint King Eric for it.

The point of time when the attack took place has been somewhat disputed. Attempts have been made to date the attack either to 1239 or to 1256. Neither date has received wide acceptance.

Background
Sweden's sudden determination to take over Finland has not been explained, but for one reason or another Finland was high on Birger Jarl's agenda. Finland became an integrated part of Sweden since there was a lot of exchange between the regions, especially via the Åland archipelago. During those days, it was easier to travel by sea than by land. Birger Jarl seems to have headed for Finland just after having both crushed the Folkung uprising of 1247-1248 and finalized the Treaty of Lödöse with Norway earlier in the summer of 1249.

Sweden's previous attempts to gain a foothold in Estonia in 1220 may have urged Sweden to settle with what was still available. Eric's Chronicle also points out the threat from Russians, mentioning that the "Russian king" had now lost the conquered land.

Target of the crusade
All details of the crusade are from Eric's Chronicle, which is largely propagandist in nature, written amidst internal unrest and war against Novgorod. The chronicle has caused a long controversy on the actual target of the expedition, since it presents Tavastians (taffwesta) as the Swedish opponents. Based on this, it is usually assumed that the target of the crusade was also Tavastia, even though that is not explicitly said in the chronicle. Tavastians are known to have rebelled against the church in the 1230s, which had resulted in a papal demand for a crusade against them in a letter in 1237.

According to the chronicle, the expedition was prepared in Sweden and then conducted over sea to a land on the coast, where the enemy was waiting. Since Tavastia was inland, this contradiction was later explained so that there was a Tavastian port somewhere on the coast that was the primary target of the attack.

Chronicle also mentions that a castle called "taffwesta borg" was established after the war. There have been lot of attempts to identify the castle with either Häme Castle or Hakoinen Castle in central Tavastia, but neither has been indisputably dated to such an early period. The first Swedish garrisons in Finland seem to have been in a hill fort later called as "Old Castle of Lieto", not far from Turku and Koroinen, the fortified church-residence of the early bishops, along the Oxen Way to central Tavastia.

Church reaction and reorganization
Probably related to preventing other parties from getting involved in the conflict, Pope Innocent IV took Finland under his special protection in August, 1249, however without mentioning Sweden in any way. Finland's bishop Thomas, probably a Dominican monk, had resigned already in 1245 and died three years later in a Dominican convent in Gotland. The seat being vacant, the diocese had probably been under the direct command of the papal legate William of Modena whose last orders to Finnish priests were given in June, 1248.

Swedish Bero was eventually appointed as the new bishop in 1248/9, presumably soon after William's visit to Sweden for an important church meeting at Skänninge that ended on March 1, 1248. The so-called "Palmsköld booklet" from 1448 noted that it was Bero who gave Finns' tax to the Swedish king. Bero came directly from the Swedish court like his two successors. It seems that Swedish bishops also held all secular power in Finland until 1280s when the position of the Duke of Finland was established.

In 1249, the situation was also seen clear enough to have the first Dominican convent established in Finland. There had been no monasteries in Finland before that. The convent was situated next to the bishop's fortification in Koroinen until the end of the century.

Aftermath
As an unexpected side effect, the expedition seems to have cost Birger the Swedish crown. As King Eric died in 1250 and Birger was still absent from Sweden, the rebellious Swedish lords selected Birger's under-aged son Valdemar as the new king instead of the powerful jarl himself.

From 1249 onwards, sources generally regard Finland as a part of Sweden. Diocese of Finland is first listed among the Swedish dioceses in 1253. In Russian chronicles, the first reliable mention of Finns being a part of Swedish forces is from 1256. However, very little is known about the situation in Finland during the following decades. Reason for this is partly the fact that Finland was now ruled from Turku and most of the documentation remained there. As the Novgorod forces burned the city in 1318 during the Swedish-Novgorodian Wars, very little remained about what had happened in the previous century.