[6] All details of the crusade are from Erik's Chronicle, which is largely propagandist[citation needed] in nature, written a century after the events, amidst internal unrest and a war against Novgorod.

The chronicle places the crusade between the Battle of Sparrsätra in 1247 and the death of King Erik Eriksson in 1250, and presents the pagan Tavastians (the hedna taffwesta) as the Swedes' opponents.

[9] The so-called "Detmar Chronicle", originating from Lübeck around the year 1340, confirmed the expedition with a short note that Birger Jarl submitted Finland under Swedish rule.

[11] Unlike the dubious First Swedish crusade, there seems to be little doubt that Sweden's effort to Christianize Finland reached a culmination in the middle of the 13th century.

Although the chronicles attempted to paint the Crusade as a war of conquest, it was likely more of an unusually bloody phase in the ongoing process by which Finland was incorporated in the Swedish state.

In the 16th century, Mikael Agricola dated the crusade to 1248, while Paulus Juusten gave the year as 1249 in one edition of Chronicon episcoporum finlandensium (Bishop Chronicle).

[14][18] Gallén's dating would also place the crusade before the unsuccessful expedition to the Neva, in which the Swedes were beaten by the Novgorodian prince Alexander Nevsky.

[13][17] However, Nordstrandh has pointed out that the author of Erik's Chronicle usually emphasizes the title jarl, but when describing the crusade Birger is only presented as the king's brother-in-law and a forman of the expedition.

[13] The only Russian source to mention "Berger" as the leader of the Neva campaign is the apocryphal Testament of the Swedish King Magnus from the mid-14th century.

John H. Lind has argued that in other cases the Testament contains historically accurate details, and cannot be refuted as a reliable source with respect to the Neva campaign.

[13] Probably in an effort to prevent other parties from getting involved in the conflict, Pope Innocent IV took Finland under his special protection in August 1249 but without mentioning Sweden in any way.

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.

[23] 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 1 March 1248.