After the death of the 3rd Caliph Osman...
After the death of the 3rd Caliph Osman, Husain’s father ‘Ali (as) was compelled by the people of Madinah overwhelmingly to take the reigns of power. ‘Ali (as) was reluctant and waited for three days before accepting the mantle of worldly power along with the authority of Imamah. (see life of Imam ‘Ali ) (as) . Circumstances changed rapidly and within the first 6 month of ‘Ali’s Khilafat he had to leave Madinah for Basra and the battle of Jamal took place.
We see that Husayn (as) who took no part in any battles before was a commander of ‘Ali’s forces in this first battle under his father’s leadership. Fighting began and ended in just one day, the battle was over, ‘Ali (as) performed funeral prayers on dead of both sides and buried them. Victors and vanquished were treated the same way. Hazrat Ayesha was returned to Madina under the escort of her brother Muhammad Ibne Abibakr and 40 other men.
She repented her participation in the battle all her life and never forgave Talha and Zubair who deceived her into this battle against ‘Ali (as). She also realized that the true instigator of this battle was Muawiya under whose directions both Talha and Zubair started this whole adventure against the legitimately elected Caliph of Islam. It was to destabilize the power base of Islam which was the Khilafat of ‘Ali (as) When he did not succeed in this he began other tactics to do thsame.
His bands of soldiers raided many parts of Iraq to burn and loot villages and destroy communities. ‘Ali (as) had no choice but to prepare for battle with Muawiya. The battle of Siffin took place in the 2nd year of ‘Ali’ (as) Khilafat and Husayn (as) took full part. He was the commander of a garrison of 10,000 men along with his elder brother Hasan (as) and Muhammad (Hanafiya).
It was ‘Ali’s practice to put his other son Muhammad-e-Hanafiya in the forefront and save the lives of these two grandsons of the Prophet. Nevertheless they took full part in these battles and fought with great bravery. The 3rd battle during the Khilafat of ‘Ali (as) was the battle of Nehrwan fought against the Khawarij. This was also over in just one day with total defeat of Khawarij. ‘Ali (as) returned to Kufa and the main administration of the Islamic Welfare State began.
Both brothers were the chief administrators of this Welfare State where they would seek out those poor adestitute within the state and provide them with the necessities of life.