Scotland, from the point of 1087 on, was a place of great turmoil. King Malcolm had just recently died, and his two sons were on the brink of civil war. The rightful heir, Prince Edward, was supported by the nobles of Scotland, and could be guaranteed the support of Edinburgh, Oslo, and Dublin if worst came to worst. The usurper was named Edmund Canmore. He was supported by the English, as he favored becoming their vassal. However, he could not realize this wish while his brother had a claim to the throne. If he decided to attempt to take the throne by force, the inhabitants of York and Inverness would aid him.
In December 1089, Prince Edward returned from Oslo with his veteran troops to begin his coronation. Edmund, predictably, blocked his entrance to Edinburgh, insultingly flying the English flag over the city. The local Scots took great offense to this, and forced him out of the city with a ragtag band of troops. It was at this time that Edmund decided to seize, or attempt to seize, the throne of Scotland. His troops, flying the English flag and wearing English colors, attacked Prince Edward.
Waiting for the enemy...

Edmund the Usurper approaches...

The opening "shots" of the civil war.

Flank them!

The cowardly dogs run!
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After the decisive first battle, in which Edward won a heroic victory, Edmund retreated to York, bringing his tired and hungry army with him. The citizens of York greeted him as a liberator, for they had been the ones to whom the English were closest. Because of this fact, and the fact that most English hated Scots, the English had conducted brutal raids into the area around York, depriving them of their food and supplies.
However, when Edmund became lord of York, the English took a more kindly glance to his breakaway empire, as evidenced by the equipment which he and his army received in large shipments from England. With these, even the militarily inexperienced Edmund was able to pose a threat to Edwards armies.