In the 12th century the boundary between England and Scotland was open to great dispute, but in the late 1130s England was also descending into Civil War, between Stephen and Matilda. Through the centuries when the English have been involved in foreign or civil wars the Scots, in normal times the weaker military force, have often exploited this weakness. But in 1138 king David of Scotland was also a relative and close supporter of Matilda, the contender for the English throne. His invasion therefore had support of some of the northern English lords and his intention was conquest and control of the northern counties not simply plunder and destruction.
In several invasions between 1136 and early 1138, he had taken control of the border counties. In August 1138, with King Stephen involved in military action in the south of England, David once again took the offensive. But when he marched into Yorkshire he was countered by a large, well armed English force raised by the Archbishop of York. In this situation early medieval armies and especially Scottish forces, because usually less well armed and equipped than the English, would normally avoid battle. At Northallerton king David, perhaps in confidence of his numerical superiority, took the offensive. In the first battle between the two kingdoms since the Norman Conquest the Scots suffered a dramatic defeat.