The consequences of both the tragedies were fatal, but the consequences of the tragedy of the assassination of Uthman were more grimfull. The tragedy of Karbala did h~ have much of political repercussions. The Umayyads instead of being dislodged came to be further entrenched in power. The Alids did not succeed in their bid to capture power. Even when the Ummayyads were overthrown in 750 C.E., power was captured by the Abbasids and not the Alids. The tragedy of Karbala thus did not have any repercussions on Islamic polity.
The tragedy of the assassination of Uthman had, on the other hand, immense repercussions on the Islamic polity. With the assassination of Uthman the process of the expansion of Islam came to a grinding halt. Uthman was assassinated when the Muslims were poised for further advance against the Christian powers in Asia Minior and Europe. But for the assassination of Uthman, the bluslims would not have been involved in civil war, and the resources that, were wasted or in civil war could have been used with advantage in winning further conquests against non-Muslims.
It is strange thatt he memory of the tragedy of Karbala is kept alive by Moharrum celebrations every year, but the memory of the tragedy of the assassination of Uthman is not kept alive in the way. it should have been kept commensurate to the historical importance of the event.