This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The Second Fitna was fought explicitly over who held legitimate authority within the Muslim community after Mu'awiya's own death, and its central episode, the killing of Husayn ibn Ali at Karbala in 680, became the founding martyrdom narrative of Shia Islam itself, fixing a lasting doctrinal and political division between Sunni and Shia Islam that has continued to shape the religion's history down to the present day.
Karbala is commemorated annually by Shia Muslims on Ashura as the founding act of Shia identity and its own distinct understanding of rightful leadership through the Prophet's family line, a religious meaning that long outlived the military contest which first produced it thirteen centuries ago. The war's outcome also cemented Umayyad dynastic succession over the earlier elective caliphate model that had preceded it, a political consequence that ran alongside, and was ultimately outlasted by, its deeper and more enduring religious one. The Sunni tradition, for its part, generally reads Karbala as a tragedy within a single shared community rather than as the founding wound of a separate confessional identity, one of the clearest points on which the two traditions' own historical memory of the same day continues to diverge.