The Danish Civil Wars (, ) were a series of civil wars fought in the Kingdom of Denmark, first from 1131 to 1134 over the murder of Canute Lavard, then from 1139 to 1143, and finally a war of succession fought from 1146 to 1157, after the abdication of Eric III of Denmark, the only monarch in Danish history to have abdicated. The first phase of the war was fought between King Eric II of Denmark and King Niels joined by Magnus the Strong. The second phase of the war was fought between the son of Eric III, Canute V of Denmark, the son of Eric II of Denmark, Sweyn III of Denmark, and his cousin Valdemar I of Denmark, son of Canute Larvard. The civil wars marked an increase in the influence of the Holy Roman Empire in Denmark, and for a time after, Denmark was a vassal state of Emperor Frederick I. The war ended with the deaths of seven kings. Two of the kings, Olaf Haraldsen and Magnus the Strong, are not amongst the official Danish line of kings. The other kings are Niels I, Eric II, Eric III, Canute V and Sweyn III.
Background
In the 11th century, Denmark had historically been an elective monarchy, and even though for the most part the eldest would inherit, it still left the possibility of succession crises. Sweyn II Estridsen would end up fathering sixteen sons, of which five would sit on the throne: Harald III, Canute IV, Olaf I, Eric I, and Niels. In the 30 years of Niels' reign, 26 would be in relative peace and prosperity. He was known for his frugality and piety, even among his critics such as Saxo Grammaticus. He granted his nephew, Canute Lavard, the title of Duke of Schleswig and gave him further opportunities to expand his domain. Canute distinguished himself in this role, as he was not only able to defend the southern border, but he was also able to subjugate the Obotrites. Canute was renowned for his charisma, chivalry and honour, and is remembered as a virtuous and modest man. He was also a strong candidate for being the next king, as he enjoyed support from the powerful house of Hvide, who raised him, and from Holy Roman Emperor Lothair III, who granted him the title Duke of Holstein for his campaigns against the Wends. King Niels and Canute had a cordial relationship, however relations between Canute and the son of Niels, King Magnus the Strong of the Geats, were colder.
The Feud of 1131–1134
On 7 January 1131, Magnus lured Canute Lavard into the Haraldsted Forest, a little north of Ringsted, where he was murdered. Soon after, civil war broke out when Canute Lavard's half-brother, Eric II, gathered his late brother's levies to avenge him. Eric demanded that Magnus be brought to justice for the murder of his brother or the king would face open revolt. His forces stopped not far from Jelling, by the Bishop of Ribe, who urged patience and insisted on the king's innocence. This was all a ruse, however, as King Niels was able to gather the support of the Jutlandic nobles, and rout the forces of Eric completely at the Battle of Jellinge Heath. Eric was therefore forced to flee east, leaving southern Jutland defenseless. Without any aid Southern Jutland surrendered swiftly, meanwhile Eric II traveled to the Holy Roman Empire to gain the support of Holy Roman Emperor Lothair III. Lothair III marched north with an army of 6000 men, joined by a naval force under Eric to relieve the city of Schleswig from a siege. During the ensuing battle, Lothair deserted after coming to an agreement with Magnus and Niels in which they agreed to pay a large sum of money and abandon Lund as an independent archdiocese and place it under Hamburg-Bremen. Eric II managed to convince a force under Adolf II of Holstein to stay, but they were still decisively defeated by forces under Magnus the Strong. Despite these heavy defeats, the continued support of the nobles of Zealand, such as the Hvides and Peder Bodilsøn, would cause figures such as the Archbishop of Lund, Asser Thorkilsson, as well as several members of the Jutish nobility, to swing over to Eric II's side. With the open revolts to the north, Niels split his forces and named Magnus commander of the navy. Niels planned to crush the rebels in the north while aiming for Magnus to destroy Eric and his fleet. Magnus searched for some time along the coast of Zealand, however, after finding little he relaxed his search. Eric seized the opportunity and almost completely annihilated Magnus' fleet at the Battle of Sejerø. Eric's navy then raided along the Limfjord, landing many troops around Himmerland and sacking Viborg, where the local bishop Eskild– a supporter of Niels– was murdered during his morning service in the year 1132.