Also, understand that when Sayyadi Imam Hussian started his journey towards Karbala, he knew exactly well that he is going towards his death. He gave dozens of Khutbas on the way to Karbala and told all the allies, supporters, Shias that they were heading towards their death and people should leave if they want to live ! Thousands left him on the way... only the 72 family members and die hard followers remained with him in Karbala. Thousands others either left him on the way or refused to come... 

Why did Imam Hussain made this journey ?? Knowing fully well that he is heading towards certain death, especially when he also knew about the Hadees from Sayyadi Rasul Allah ?? Was it to gain power ?? was it to win in the battle ?? 

Yazeed was NOT sunni. He was NOT shia. He was an enemy of Rasul Allah (sm), an enemy of Islam, an enemy of Agl Beyt, who had changed the very foundations of Islam at that time, just as King Akbar tried to do in India many centuries later. That is why Imam Hussain refused to give his Bayt to Yazeed, just as Mujaddid alf e Sani refused to show loyalty to Akbar on sunnah of Imam Hussain.