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IOTL, Saladin was declared sultan of Egypt after waging war against it in Syria's name. Nur ad-Din, leader of Syria wanted more controle over Egypt, but Saladin stalled. Understandably this lead to conflict between the two and they raised their armies to battle it out. Some days before the big battle, Nur ad-Din died and Saladin used the ensuring chaos to make himself ruler of both Egypt and Syria. Now he had the strength to retake Jerusalem and more.
Let's say Nur ad-Din lives a little longer and faces Saladin in Battle. There is no clear winner, but Saladin etablishes himself as independent sultan of Egypt. Nur ad-Din lives long enough to prepare his son for his position and the countries are not united. What happens next? Are the crusader states safe for a longer time? Will the eastern roman empire reestablish itself against weaker muslim invaders? What happens in europe, with a living Barbarossa and no ransom for Richard Lionheart?
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