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Around 1340 the Marinid Dynasty of Morocco helped the Granada Emirate against an attack by the Reconquista powers of Castile and Portugal. The Battle of Rio Salado ended in disaster for the Islamic powers and was the last major attempt by a North African and Islamic power to invade or unite the Iberian Peninsula. What if the Marinids had been a little more successful?
Say during the battle, the Islamic lines hold out better and perhaps the coup-de-grace Alfonso XI of Castile is also killed during the battle. For Castile this generates the interesting succession crisis of two under age successors and also illegitimate heirs who in OTL tried to seize the throne after Alfonso's OTL death.
Perhaps, leading to the Marinids even re-taking Seville and some other acquisitions in eastern and central Spain. Perhaps the butterflies allow Sultan Abu al-Hasan to have a better time domestically and not get deposed and breath new life into Islamic Iberia. Most likely it would not save the Marinid dynasty itself in the long run but perhaps it would save Islamic Iberia or at least add a few centuries to its shelf life.