In 937, Aethelstan, King of England (the first to truly hold the title with any merit) was faced with an invasion of a Grand Alliance of Scotland, Dublin, Strathclyde, the expelled ruler of York and others. Although caught by surprise, as the invasion occured late in the year, Aethelstan was triumphant. His victory secured, for the time, English domination of York (it would, for a short period, fall out of the crown'd hand during his successor's reign) as well as his place in history as the first true monarch of all England.
But; what if it hadn't? What if Aethelstan had been cut down in battle, along with his brother/heir Edwin?
York would have come back under the sway of the Norse, likely Olaf, and England would have been dealt a massive defeat withthe death of their King and his heir.
Would this have been enough to establish York as a Kingdom of its own, outside of the rule of England? And, if so, how would this Kingdom change the power dynamics in the isles? (extra points, if, somehow, this means Scrythclye also survives through butterflies

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