Valdemar II Sejr (the Victorious) was king of Denmark (1202-1241) in succession to his brother Knud VI.
Valdemar was born around 1168, the second son of King Valdemar I and Sophia of Minsk. In 1201 the city of Lübeck, the most important port on the Baltic Sea, submitted to Valdemar after a period of Danish expansion in northern Germany, partly due to Valdemar’s efforts in the area as duke of Schleswig in the 1190s. By the beginning of the thirteenth century Denmark under Valdemar was a naval superpower, since all of the southwestern shores of the Baltic Sea as far as Prussia had yielded to Danish rule.
Despite a remark in the chronicle of Henry of Livonia, it is doubtful whether Valdemar took part in an abortive crusade against the island of Osel (mod. Saaremaa, Estonia) in 1206, as other sources report him to have been militarily engaged in Germany at the same time. However, following crusades to Livonia in 1217 undertaken by Valdemar’s vassal Count Albert of Orlamünde, Bishop Albert of Riga asked for support from Valdemar in 1218. The ensuing agreements secured (at least temporarily) Danish royal recognition of Albert of Riga. In the summer of 1219 a royal Danish army conquered the northern parts of Estonia, where Valdemar swiftly introduced a Danish administration.
To secure his position against Danish claims, Albert appealed to Pope Honorius III, who confirmed the bishop’s right to Estonia and the Livonian provinces of Selonia and Semgallia. However, in 1221, following a Danish blockade of Lübeck lasting over a year, Albert of Riga was forced to accept Valdemar’s lordship over Estonia and Livonia as well as Valdemar’s bestowal of land on the Order of the Sword Brethren. In 1222 Valdemar conquered Osel in a campaign joined by Albert of Riga and the Sword Brethren, and negotiations between the three parties led to a division of Estonia. Valdemar still claimed overlordship over the whole country, but retained direct rule only over the northern provinces. He ceded the central and southern provinces to the Sword Brethren, and granted spiritual rights there to the bishop of Riga. He gave up his claims to Livonia proper.
The Estonians of Osel had not been fully subjected and soon revolted against Danish rule. The rebellion spread to the mainland, with the result that all the Danish conquests in Estonia were lost with the exception of the town of Reval (mod. Tallinn). At the same time Valdemar was taken hostage by one of his northern German vassals, Count Henry of Schwerin (May 1223). This incident effectively halted Danish expansionist politics. Although Valdemar was released from captivity after payment of a large ransom (1225), his defeat by the forces of Lübeck and its allies at the battle of Bornhoved (1227) marked the end of Danish supremacy in the Baltic region. Valdemar worked hard to regain power in Estonia, and the Christian powers in the Baltic region finally agreed on a division of Estonia in the Treaty of Stensby (1238). A royal cadastral work from the 1230s gives details of the Danish administration of Estonia.
Valdemar’s two marriages, to Dagmar (Margaret) of Bohemia (1205) and Berengaria of Portugal (1212), reflect the level of international recognition accorded to the Danish king at the beginning of the thirteenth century.