The War of the Alfar, also known as the South Jórvík Civil War, was a conflict between Alfr Ormarsson, son of the previous king of Wessex, and Alfr Guðfriðsson, the late king Ormar's brother, over the succession of the Kingdom of Wessex. At the time of Ormar's death, his son Alfr was young and largely untested, prompting a majority of nobles in Wessex to support his uncle, also named Alfr, as Ormar's successor. Alfr Ormarsson's refusal to give up his claim to the throne led to the outbreak of war, which eventually engulfed many of Wessex's nearby neighbors.
In 950 Alfr Guðfriðsson would be killed at the Battle of Long Knoll, cementing Alfr Ormarsson's rule as king of Wessex. The War of the Alfar would leave Wessex heavily weakened, ending the period of expansion into central Britain, often at the expense of Jórvík itself, that had been begun by Ormar.
Ormar Guðfriðsson, King of Wessex, one of the most influential subkings in the Kingdom of Jórvík, died in 948, leaving his young son Alfr to succeed him. Alfr was largely unproven as a leader at this time, and would be inheriting a large domain stretching from the English Channel into central Mercia. Concerns over the competence of this young ruler led to many nobles in the south supporting Ormar's brother, also called Alfr. Alfr Guðfriðsson had proven himself a warrior during previous wars, and already ruled over a sizable domain under Ormar, making him a likely choice. Alfr Guðfriðsson assembled a small army from those who supported him, and marched to Winchester to push his claim. He found that his nephew had already raised an army of his own and had left the city.
Alfr Guðfriðsson was declared king in Winchester, despite the protests of the younger ruler, who now fled north and attempted to raise support from those who had fought under his father. Both parties met for the first time near Swindon, where despite being outnumbered, the young Alfr was able to outflank his uncle, causing a large number of casualties to the defending force. Ultimately Alfr Ormarsson would be forced to retreat, however his leadership in the battle would prove himself competent, and helped him gain additional support. This was in combination to a successful raiding campaign, in which Alfr Ormarsson raided towns loyal to his uncle, often Anglo-Saxon communities. Later that year Halfdan Ragnarrsson, son of Ormar's former ally, the King of Cornwall, swore to aid Alfr Ormarsson, and marched east into territory held by Alfr Guðfriðsson.
Alfr Guðfriðsson responded by marching west and chasing after Halfdan into 949. They finally met at Yeovil, where Alfr achieved a crushing victory against the Kingdom of Cornwall. Halfdan's kinsman Harthacnut was killed in the battle, as was a large portion of Halfdan's army. Although the battle would prove a crushing defeat for Halfdan, the battle did weaken Alfr Guðfriðsson's own forces, as well as distracting him from Alfr Ormarsson in the east. This allowed the young Alfr to raise his forces, as well as secure support from lords across Jórvík. King Rögnvaldr of Jórvík led a number of raiding parties into the south to take advantage of the situation, which although were indirectly beneficial to Alfr Ormarsson, were largely motivated by a separate goal for personal expansion.
Wessex would be permanently reduced in terms of territory in the east, as Jórvík captured a number of towns on the southern coast of Britain, trapping Alfr Guðfriðsson in central Wessex. After a successful siege Alfr Ormarsson would successfully capture Winchester, being properly crowned king. This would be a crushing blow to Alfr Guðfriðsson, who now fought defensively from multiple foes. At the Battle of Long Knoll both sides met once more commanded by Alfr Guðfriðsson and Alfr Ormarsson respectively. Alfr Guðfriðsson would put up a valiant defense, but would ultimately be killed, effectively ending the war. That year Alfr Ormarsson was officially recognized as king of Wessex, and later swore allegiance to Rögnvaldr, king of Jórvík.
The War of the Alfar would devastate much of southern Jórvík, weakening the once powerful kingdom established by Ormar. The war potentially prevented Wessex from further expanding into central Britain, something that Ormar had done against the earlier kings of Jórvík. Instead Wessex would largely turn to the Welsh kingdoms to the west, further weakening and distracting Wessex from greater ambitions over Britain. Jórvík itself would be able to benefit from the war, although Sigfrið Rögnvaldrsson, Rögnvaldr's oldest son, would be killed in the fighting, leaving Styrbjörn has his next logical heir.