According to the Eric’s Chronicle, Birger Jarl wished to succeed Eric, but had to step aside for his son, who was of royal descent through his mother, King Eric’s sister. But Birger Jarl remained the all-powerful, although uncrowned, ruler till his death.
Many of the nobles were not satisfied with the election of Valdemar. They joined forces, gathering hired troops from Denmark and Germany. Birger met them at Hervadsbro and defeated them, capturing the leaders, who were beheaded. Among these were Philip, a son of Knut the Tall, and Knut Magnusson, with others of the Folkung family, which often was at war between themselves when great interests were at stake.
After this battle peace reigned under the powerful and sagacious rule of Birger. An assault upon Denmark by King Hakon of Norway and Birger jointly was planned, but a peace agreement took its place, in 1253. In the further complications between Norway and Denmark, Birger took no part. When later King Christopher of Denmark called upon his northern neighbors for help against revolts in his own country, these were ready to respond; but at the sudden death of King Christopher these plans were frustrated. In 1260 Birger bettered the already friendly relations with Denmark, by arranging the marriage between King Valdemar and the Danish princess, Sophia, whereupon he, himself a widower, married Mechtild, a queen-dowager of Denmark. In Finland, conditions were the same as of yore, pagan tribes and Russian invasions rendering everything unsafe and perilous. Birger renewed the trade agreement with Lubeck, in 1251, with added privileges to Lubeck, but with the stipulation that those of its citizens who settled in Sweden must become Swedish subjects. In 1261 the same privileges were extended to Hamburg. It was at this period that the Hanseatic League was formed between the commercial centres of North Germany. The relations between the league and the Scandinavian countries waxed quite intimate and, at times, menacing to the political independence of the latter. But Sweden derived many benefits through the contact with the reviving culture of Southern Europe, which was brought about through the Hanseatic League; the newly opened mining industry and the prosperity of Swedish commercial centres particularly owing much to this influence. Stockholm became the largest and most important of Swedish towns during the days of Birger, although he was not its founder. Also with England, Birger was carrying on peaceful proceedings; yet their purpose is not known. In 1237, the king of England had granted the merchants of the island of Gothland free trade privileges. Birger was a great and sound legislator, although it is not known with certainty how many of the judicial reforms accredited to him originated in these days. He made the law that sister should have equal share of inheritance with brother, and the laws of sanctity of home, Church, Thing and woman, which formed the kernel of a set of laws, later called _Edsœre_ (Pledged oath), which every crowned king and his foremost men must pledge themselves to uphold. He tried to make away with the ordeal of walking on, or the handling of, iron as a legal testimony of guiltlessness. Further, he prohibited the custom of self-imposed thraldom.