Final answer:
The provided question about King Arthur returning to his kingdom after murdering the regent is likely fictional, but historically, monarchs returned due to invasions, political unrest, economic crises, and natural disasters.
Step-by-step explanation:
The question 'What was the emergency that made King Arthur rush back to his kingdom even though he had murdered the regent?' does not align with any historical account of King Arthur and seems to be a fictional scenario.
To provide an accurate response, we would need context specific to the storyline from which this scenario comes. However, based on historical crises that have been proven to compel leaders to return to their kingdoms, the most common emergencies include invasion by a neighboring kingdom, political unrest, economic crisis, and natural disasters.
Considering the context provided in the reference information, during times like the War of the Roses and the Tudor dynasty, both political unrest and foreign invasions were key issues that would necessitate a monarch's presence. Moreover, economic crises were frequent causes of turmoil as indicated in discussions about the French Revolution