From The Rise and Fall of the Danish Empire, by Michael Bregnsbo and Kurt Villads Jensen (Palgrave Macmillan, 2022), Kindle pp. 103-105:
On Christmas Day 1144, the Christian Principality of Edessa was lost to Sultan Zenghi of Mosul. It was the first major defeat in the Latin Middle East, and when the news reached Western Europe, it was met with despair and determination. Something had to be done, and preparations were underway for a new crusade just as large as the first (in general, see Phillips 2007). An absolutely crucial force in this effort was Bernard of Clairvaux, abbot of the wide-reaching Cistercian order. Bernhard was a gifted speaker and traveled throughout northern Europe on a preaching mission, and it was also he who initially allowed Northern German princes to fight the pagan Slavic peoples instead of traveling to Edessa. He rationalized this on the theological grounds that the devil attacked Christianity on all fronts simultaneously, and that it was just as important to defend themselves in the north as it was in the south. This cumulatively led to the so-called Second Crusade in 1147, which was one crusade but executed on many fronts, as it was described by contemporaries. Crusades were led against Damascus, against several places in the Iberian Peninsula, and in the Baltic Sea.
In 1146, Cardinal Ubaldus hosted a church meeting in Odense to preach crusade and drum up support (Bysted et al. 2012; Jensen 2017). The reaction must have amazed him, because King Erik III Lamb of Denmark immediately abdicated and entered a monastery, thus becoming the first and so far the only Danish king to voluntarily surrender the throne. He also died shortly afterwards and presumably resigned due to illness. He was followed by Sweyn III, who was later nicknamed Sweyn Grathe. Grathe was chosen by the Sealanders, but the people of Jutland concurrently chose Canute, the son of Magnus (Nilsson) (who had killed Canute Lavard). The third individual to partake in the battle for the throne was Canute Lavard’s son, Valdemar, who was now about 15 years old. The struggle developed into an eleven year war between Sweyn III, Canute, and Valdemar, and is often portrayed as a civil war. It is probably more accurate to see the conflict as formerly independent countries who now seized the opportunity to choose their own king. Conversely, these kings sought to expand their own power and unite the kingdoms over which their predecessors had ruled. During this same time period, several kings fought for power in Norway and Sweden as well.
The bloody wars in Denmark give a rare insight to the rulers’ paths, both physically and mentally, to power within the empire. Sweyn III began his king’s reign by working with Valdemar to declare Canute Lavard a saint and place his bones as relics upon the high altar in Ringsted. It was not recognized by Archbishop Eskild because it was a private canonization without the pope’s acceptance, but it does show that Valdemar would henceforth use his father’s miracles as an argument to support his own position as king. After that, Keld of Viborg, who had previously sought the pope for permission to mission and become a martyr among the pagan Wends, mediated between Sweyn and Canute by having them participate in a joint crusade against the Wendish Dobin, near present-day Rostock. They participated because the pope promised that if they fell, their souls would be in heaven before their blood cooled on the earth (Knytlingesaga 1919–25, 108). At Dobin, they met with a Saxon cavalry, and succeeded in occupying the city, baptizing the inhabitants and forcing them to free their Christian slaves. Then, according to Saxo, the Danish army withdrew because Sweyn and Canute did not trust each other. According to his contemporary, German historian Helmold of Bosau, retreat was because “the Danes are mighty warriors at home, but completely useless in real battle” (Helmold 1868, 65).