Question: The forces of Olaf Guthfrithson were defeated by the English led by Æthelstan at a battle fought in which year ?

Context paragraphs:
Olaf Guthfrithson: Olaf Guthfrithson (Old Norse: "Óláfr Guðrøðsson" ; ; Old Irish: "Amlaíb mac Gofraid" ; died 941) was a Viking leader who ruled Dublin and Viking Northumbria in the 10th century.  He was the son of Gofraid ua Ímair and great-grandson of Ímar, making him one of the Uí Ímair.  Olaf succeeded his father as King of Dublin in 934 and succeeded in establishing dominance over the Vikings of Limerick when he captured their king, Amlaíb Cenncairech, in 937.  That same year he allied with Constantine II of Scotland in an attempt to reclaim the Kingdom of Northumbria which his father had ruled briefly in 927.  The forces of Olaf and Constantine were defeated by the English led by Æthelstan at the Battle of Brunanburh.

Battle of Pima Butte: The Battle of Pima Butte, or the Battle of Maricopa Wells, was fought on September 1, 1857 at Pima Butte, Arizona near Maricopa Wells in the Sierra Estrella.  Yuma, Mohave, Apache and Yavapai warriors attacked a Maricopa village named Secate in one of the largest battles in Arizona's history.  It was also the last major battle fought by the Yumas and the last major battle fought solely between native Americans in North America.

Battle of Byeokjegwan: The Battle of Byeokjegwan (or Pyŏkje) (Chinese: 碧蹄館大戰; "Bì tí guǎn dàzhàn") was a battle fought on January 27, 1593 (January 26 according to the Japanese calendar of the time), between the armies of the Ming Dynasty led by Li Rusong, and the Japanese forces under Tachibana Muneshige, Ukita Hideie, and Kobayakawa Takakage.  As part of the Japanese Invasion of Korea (Imjin War), it was the first field battle fought during the war between the two sides.

Battle of Brentford (1016): The Battle of Brentford (1016) was fought in 1016 some time between 9 May (the approximate date Canute landed at Greenwich) and 18 October (the date of the later Battle of Ashingdon) between the English led by Edmund Ironside and the Danes led by Canute.  It was one of a series of battles fought between Edmund and Canute, ultimately resulting in the lands held by Edmund's father Ethelred the Unready being divided between the two.  Edmund was victorious in this particular battle, but ultimately failed to defend the lands inherited from his father.

Battle of Brunanburh: The Battle of Brunanburh was fought in 937 between Æthelstan, King of England, and an alliance of Olaf Guthfrithson, King of Dublin; Constantine, King of Alba and Owen, King of Strathclyde.  One of the historiographical cruxes of this battle is the fact that it is often attributed to as the point of origin for English nationalism.  Additionally, historians such as Michael Livingston argue that "the men who fought and died on that field forged a political map of the future that remains [in modernity], arguably making the Battle of Brunanburh one of the most significant battles in the long history not just of England, but of the whole of the British Isles."

Olaf Guthfrithson (disambiguation): The English Olaf Guthfrithson is a form of the Old Norse Óláfr Guðfriðarson.  An Anglicised form of the Old Norse name is Olaf Godredsson.  The Old Irish form of these names is Amlaíb mac Gofraid.  These four names may refer to:

Battle of Párkány: The Battle of Párkány (Turkish: "Ciğerdelen savaşı" ) (October 7–9, 1683) was a battle fought in the town of Párkány (today: Štúrovo), in the Ottoman Empire, and the area surrounding it as part of the Polish-Ottoman War and the Great Turkish War.  The battle was fought in two stages.  In the first stage Polish troops under John III Sobieski were defeated by the Ottoman army under Kara Mehmed Pasha on October 7, 1683.  In the second stage Sobieski, supported by Austrian forces under Charles V, Duke of Lorraine, defeated the Ottoman forces, which were supported by the troops of Imre Thököly, and gained control of Párkány on October 9, 1683.  After the defeat Austrians would besiege Esztergom and captured it at the end of 1683.

Battle of Inō: The Battle of Inō was a battle fought during the Sengoku period (16th century) of Japan.  The battle was fought between two forces of the Oda clan, the head of the clan Oda Nobunaga and his brother Oda Nobuyuki, who with the support of Shibata Katsuie and Hayashi Hidesada, rebelled against Nobunaga.  The three conspirators were defeated at the Battle of Inō, but they were pardoned after the intervention of Tsuchida Gozen, the birth mother of both Nobunaga and Nobuyuki.  The next year, however, Nobuyuki again planned to rebel.  When Nobunaga was informed of this by Shibata Katsuie, he faked illness to get close to Nobuyuki and assassinated him in Kiyosu Castle.

Raven Penny: The Raven Penny is a coin of the Viking Olaf Guthfrithson who was the king of Dublin between 934-941.

Harald Sigtryggsson: Harald Sigtryggsson (Old Irish: "Aralt mac Sitric" ; Old Norse: "Haraldr" , died 940) was a Viking leader who ruled Limerick in the early 10th century.  He was the son of Sitric Cáech and great-grandson of Ímar, making him one of the Uí Ímair.  He was installed as king of Limerick following the capture of the previous king Olaf Scabby-head by Harald's cousin Olaf Guthfrithson, king of Dublin, during a battle at Lough Ree in 937.  Harald died in 940 and was ultimately succeeded by Ivar of Limerick.

Supporting paragraphs: Olaf Guthfrithson Battle of Brunanburh
Answer: 937