Anti-Shi'ism is the prejudice against or hatred of Shia Muslims based on their religion and heritage. The term was first defined by Shia Rights Watch in 2011, but has been used in informal research and scholarly articles for decades.
The dispute over the right successor to Muhammad resulted in the formation of two main sects, the Sunni, and the Shia. The Sunni, or followers of the way, followed the caliphate and maintained the premise that any member of Quraish could potentially become the successor to the Prophet if accepted by the majority. The Shia however, maintain that only the person selected by God through the Prophet (Hadith of the pond of Khumm) could become his successor, thus Imam Ali became the religious authority for the Shia people. Militarily established and holding control over the Umayyad government, many Sunni rulers perceived the Shia as a threat – both to their political and religious authority.
The Sunni rulers under the Umayyads sought to marginalize the Shia minority and later the Abbasids turned on their Shia allies and further imprisoned, persecuted, and killed Shias. The persecution of Shias throughout history by Sunni co-coreligionists has often been characterized by brutal and genocidal acts. Comprising only around 10-15% of the entire Muslim population, to this day, the Shia remain a marginalized community in many Sunni Arab dominant countries without the rights to practice their religion freely or to become established as an organized denomination.
The grandson of Muhammad, Imam Hussein, refused to accept Yazid I's rule. Soon after in 680 C.E., Yazid sent thousands of Umayyad troops to lay siege to Hussein’s caravan. During the Battle of Karbala, after holding off the Umayyad troops for six days, Hussein and his seventy-two companions were killed, beheaded, and their heads were sent back to the caliph in Damascus. These seventy-two included Hussein's friends and family. The more notable of these characters are Habib (Hussein's elderly friend), Abbas (Hussein's loyal brother), Akbar (Hussein's 18-year-old son), and Asghar (Hussein's six month old infant). On the night of Ashura (which is called Sham-e-Gharibaan), the army of Yazid burned the tents which Hussein's family and friends had lived in. The only occupants of the tents after the war were the women, children, of Hussein's companions along with Hussein's last ill son named Zain-Ul-Abideen (who became the next Imam after Hussein). During the raid, Yazid's forces looted, burned, and tortured the women and children. They then took the heads of the martyrs, planting them on spearheads to parade. The women's shawls and headdresses were also stripped and they were forced to march beside their men's heads all the way to Damascus. They stayed in prison there for about a year. While Imam Hussein’s martydom ended the prospect of a direct challenge to the Umayyad caliphate, it also made it easier for Shiism to gain ground as a form of moral resistance to the Umayyads and their demands.