The events of Karbala reflect the collision of the good versus the evil, the virtuous versus the wicked, and the collision of Imam Husayn (the head of virtue) versus Yazid (the head of impiety). Al-Husayn was a revolutionary person, a righteous man, the religious authority, the Imam of Muslim Ummah.
As the representative of his grandfather Prophet Muhammad (S), Imam Husayn's main concern was to safeguard and protect Islam and guide fellow Muslims. On the other hand, the staying power of the rulers (Mu'awiya and his son Yazid) depended solely on the might of the sword. They used brute force to rule over the Muslim empire even by all possible illicit means.
Imam Husayn as head of Ahlul Bayt (a.s.) never recognized Mu'awiya nor his followers. Before him Imam ‘Ali (a.s.) had fought battles against Mu'awiya because Mu'awiya continuously violated the Islamic principles. Imam Al-Hasan (a.s.) had to swallow the bitter pill of making a peace agreement with Mu'awiya, in order to safeguard the security of the Ummah which was at stake.
Karbala was the event of Islam and the sacrifice of Imam Hussain(as) for Islam. We are here at Karbala to answer the call of Imam Hussain(as) "Hal min naseeran yan surna"...
We are here O Hussain!!