I heard somewhere that in the tragedy of Karbala some of the martyrs were those who did not consider Imam Ali (a) as their first caliph and Imam. Is that true?
Some of the martyrs were like that before Karbala like Zuhair ibn al Qayn who was previously a supporter of Othman ibn Affan, but after listening and following Imam Hussain (AS), he believed fully in Ameerul Mo'mineen and Imam Hasan and Imam Husain (AS), that is why he sacrificed his life in the way of Allah under the divine leadership of Imam Husain (AS).
Wassalam.