Prior to his death, the Umayyad ruler Mu'awiya appointed his son Yazid as his successor, contrary to the Hasan-Muawiya treaty. When Muawiya died in 680 CE, Yazid demanded that Husayn pledge allegiance to him. Husayn refused to pledge allegiance to Yazid, even though it meant sacrificing his life. As a consequence, he left Medina, his hometown, to take refuge in Mecca in AH 60. There, the people of Kufa sent letters to him, asking his help and pledging their allegiance to him. So he traveled towards Kufa, but near Karbala his caravan was intercepted by Yazid's army. He was killed and beheaded in the Battle of Karbala on 10 October 680 (10 Muharram 61 AH) by Yazid, along with most of his family and companions, including Husayn's six month old son, Ali al-Asghar, with the women and children taken as prisoners. Anger at Husayn's death was turned into a rallying cry that helped undermine the Umayyad caliphate's legitimacy, and ultimately its overthrow by the Abbasid Revolution.
The annual commemoration of Husayn and his children, family and companions occurs during Muharram, the first month of the Islamic calendar, and the day he was martyred is known as Ashura (the tenth day of Muharram, a day of mourning for Shi'i Muslims). Husayn's actions at Karbala fueled later Shi'a movements, and his death was decisive in shaping Islamic and Shi'a history. The timing of Husayn's life and death were crucial as they were in one of the most challenging periods of the seventh century. During this time, Umayyad oppression was rampant, and the stand that Husayn and his followers took became a symbol of resistance inspiring future uprisings against oppressors and injustice. Throughout history, many notable personalities, such as Nelson Mandela and Mahatma Gandhi, have cited Husayn's stand against oppression as an example for their own fights against injustice.
Husayn's maternal grandmother was Khadijah bint Khuwaylid, and his paternal grandparents were Abu Talib and Fatimah bint Asad. Hasan and Husayn were regarded by Muhammad as his own sons due to his love for them and as they were the sons of his daughter Fatima. He said "Every mother's children are associated with their father except for the children of Fatimah for I am their father and lineage." Thus, the descendants of Fatimah are the descendants of Muhammad, and are part of his family.