In so doing...
In so doing, Mu'aawiyah had aimed to set a precedent for those rulers who would follow him to appoint their successors, turning the caliphate into a dynastic rule. It is noteworthy that insisting on securing the Imam's swearing of allegiance meant giving legitimacy to the caliphate. What was Imam Hussain (a.s)'s response to that demand?
Naturally, it was turned down, not least because Hussain (a.s.) was the grandson of the Prophet (s.a.w.) and was widely known for his piety and scant regard for worldly pleasures. Upon receiving the news of the Imam's rejection, the ruling establishment issued threats to him. His response was that he would rather die than endorse Yezid's succession to the caliphate. Up to that point in time, the Imam's reaction was of the passive type to an unlawful demand.
In other words, a reaction based on piety and a reality stemming from the slogan, "There is no god but God", which makes it incumbent on the believer to say no to any illegitimate demand. That rejection was not the only reason for the Imam's revolt. There was another issue, which demonstrated the underlying principle of his revolt; it was a positive reaction. That is, after the demise of Mu'aawiyah, the people of Kufa, [Iraq] cast their memories some twenty years back, i.e.
to the days of the caliphate of Imam Ali (a.s.). Despite the fact that many of Ali's disciples were liquidated by the Umayyad terror machine, such as Hijr bin Adi, Amr bin Hamq al- Khuza'ie, Rashid al-Hijri, and Maythem at-Tammar, just to render Medina bereft of the heavyweights among the companions of the Prophet, the people called to mind how Ali (a.s.) was the example of the true Muslim and his rule a just one.
Thus, they convened in Kufa and agreed among themselves to reject the endorsement of Yezid as caliph, turning their attention to Imam Hussain (a.s.) with the offer to become their Islamic caliph. They wrote to the Imam to this effect, expressing their readiness to welcome him to re-establish the Islamic rule in Kufa. Some one hundred thousand people signed those letters. As a result, those people did not leave the Imam with any choice other than to accede to their request.
That was the positive reaction. In conclusion, it can be safely said that the true nature of the Imam's movement was a legitimate one, in that a group of Muslims initiated the action and the Imam had to provide them with his positive response.