The Battle of Karbala (Arabic: مَعْرَكَة كَرْبَلَاء, romanized: Maʿrakat Karbalāʾ) was fought on 10 October 680 (10 Muharram in the year 61 AH of the Islamic calendar) between the forces of the second Umayyad caliph Yazid I (r. 680–683), and a small caravan led by Husayn ibn Ali, second son of Ali and grandson of the Islamic prophet Muhammad, at Karbala, in modern-day southern Iraq.
Prior to his death, the first Umayyad caliph Mu'awiya I appointed his son Yazid as his successor, making the caliphate hereditary. When Mu'awiya died in 680, Yazid demanded that Husayn pledge allegiance to him, but Husayn refused and took refuge in Mecca. While Husayn was in Mecca, the people of Kufa, the center of Ali's caliphate, sent him numerous letters inviting him to overthrow Umayyad rule, and pledging their allegiance to him. Husayn first sent his cousin, Muslim ibn Aqil, to Kufa to assess the situation and the genuineness of their support. After receiving a favorable report from Muslim, Husayn accepted their invitation and traveled toward the city in response to their calls.
On his way to Kufa with about 72 men, Husayn's caravan was intercepted by a 1,000-strong army of the caliph at some distance from Kufa. He was forced to head north and encamp at the plains of Karbala on 2 October, where another 4,000-strong Umayyad army arrived soon afterwards. Negotiations failed after the Umayyad governor Ubayd Allah ibn Ziyad refused to grant Husayn safe passage unless he submitted to his authority, a condition Husayn rejected. The battle ensued on 10 October, during which Husayn was killed along with most of his family members and close companions, while the surviving members of his family were taken captive and brought first to Kufa and then to Damascus. This sparked the Second Fitna, during which the people of Kufa organized two campaigns to avenge the killing of Husayn; first by the Tawwabin, and the second by the revolutionary Mukhtar al-Thaqafi, who ruled over much of Iraq and parts of northwestern Iran for eighteen months and killed several figures responsible for Husayn's death.
The Battle of Karbala gave the early political party of pro-Alids, which had not yet developed specific theological doctrines and set of rituals, a distinct religious identity and helped transform and consolidate it into a separate religious sect. Heinz Halm writes: "There was no religious aspect to Shi'ism prior to 680. The death of the third imam and his followers marked the 'big bang' that created the rapidly expanding cosmos of Shi'ism and brought it into motion."
After the assassination of the third Rashidun caliph Uthman ibn Affan in 656, the rebels and the townspeople of Medina proclaimed Ali ibn Abi Talib, a cousin and son-in-law of the Islamic prophet Muhammad, the fourth caliph. Ali's legitimacy as caliph was denounced by Uthman's cousin Mu'awiya ibn Abi Sufyan, the long-time governor of Syria, resulting in the First Fitna. When Ali was assassinated in 661, his eldest son Hasan succeeded him but soon signed a peace treaty that handed over power to Mu'awiya on the condition that Mu'awiya be a just ruler and that he would allow his successor to be chosen through shura (consultation). After the death of Hasan in 670, his younger brother Husayn became the head of the Banu Hashim clan to which Ali and Muhammad had belonged. Though his father's supporters in Kufa gave him their allegiance, he would abide by the peace treaty between Hasan and Mu'awiya as long as the latter was alive.
In 676, Mu'awiya nominated his son Yazid as successor, a move that has been labelled as a breach of the peace treaty. With no precedence in Islamic history, hereditary succession aroused opposition from several quarters. Mu'awiya summoned a shura, or consultative assembly, in Damascus and persuaded representatives from many provinces to agree to his plan by diplomacy. He then ordered Marwan ibn al-Hakam, then the governor of Medina, where several influential Muslims resided, to announce the decision. Marwan faced resistance to this announcement, especially from Husayn, Abd Allah ibn al-Zubayr, Abd Allah ibn Umar and Abd al-Rahman ibn Abi Bakr, all of whom were sons of Muhammad's prominent companions, and could also lay claim to the caliphate by virtue of their descent. Mu'awiya went to Medina and pressed them to accede, but they still refused to support him. On his return to Damascus, Mu'awiya nonetheless convinced the people of Mecca and Medina that they had pledged allegiance, and received their allegiance for Yazid as well. There was no further overt protest against the plan for Yazid's succession. According to the historians Fitzpatrick and Walker, Yazid's succession, which was considered as an "anomaly in Islamic history", transformed the government from a "consultative" form to a monarchy. Before his death in April 680, Mu'awiya cautioned Yazid that Husayn and Ibn al-Zubayr might challenge his rule and instructed him to defeat them if they did. Yazid was further advised to treat Husayn with caution and not to spill his blood, since he was the grandson of Muhammad.
On his succession, Yazid tasked the governor of Medina, al-Walid ibn Utba ibn Abi Sufyan, to secure allegiance from Husayn and Ibn al-Zubayr, with force if necessary. Walid sought the advice of his Umayyad relative Marwan ibn al-Hakam, who suggested that Ibn al-Zubayr and Husayn should be compelled to pledge allegiance as they were dangerous, while Ibn Umar should be left alone since he posed no threat. Walid summoned the two, but Ibn al-Zubayr escaped to Mecca. Husayn answered the summons but declined to pledge allegiance in the secretive environment of the meeting, suggesting it should be done in public. Marwan told Walid to imprison or execute him, but due to Husayn's kinship with Muhammad, Walid was unwilling to take any action against him. A few days later, Husayn left for Mecca without acknowledging Yazid. He arrived in Mecca at the beginning of May 680, and stayed there until the beginning of September.
Husayn had considerable support in Kufa, which had been the capital of the caliphate during the reigns of his father and brother. The Kufans had fought the Umayyads and their Syrian Arab tribal allies during the First Fitna. They were dissatisfied with Hasan's abdication and strongly resented Umayyad rule. While in Mecca, Husayn received letters from pro-Alids in Kufa asking him to lead them in revolt against Yazid, promising to remove the Umayyad governor if Husayn would consent to aid them. Husayn wrote back affirmatively and promised to lead them with right guidance. Then he sent his cousin Muslim ibn Aqil to assess the situation in Kufa. Ibn Aqil attracted widespread support and informed Husayn of the situation, suggesting that he join them there. Yazid removed Nu'man ibn Bashir as governor of Kufa due to his inaction, and installed Ubayd Allah ibn Ziyad, then governor of Basra, in his place. As a result of Ibn Ziyad's political maneuvering, Ibn Aqil's following began to dissipate, and he was forced to declare the revolt prematurely. It was crushed and Ibn Aqil was killed. Husayn had also sent a messenger to Basra, another garrison town in Iraq, but the messenger could not attract any following and was quickly apprehended and executed.
Husayn was unaware of the change of political circumstances in Kufa and decided to depart. Abd Allah ibn Abbas and Abd Allah ibn al-Zubayr advised him not to move to Iraq, or if he was determined, not to take women and children with him. He offered Husayn his support if he would stay in Mecca and lead the opposition to Yazid from there. Husayn refused this, citing his abhorrence of bloodshed in the sanctuary, and decided to go ahead with his plan.
Husayn left Mecca with a group of fifty men and his family on 9 September 680 (8 Dhu al-Hijjah 60 AH), a day before the Hajj pilgrimage. He took the northerly route through the Arabian Desert. On the persuasion of Husayn's cousin Abd Allah ibn Ja'far, the governor of Mecca Amr ibn Sa'id al-Ashdaq sent his brother and Ibn Ja'far after Husayn to assure him safety in Mecca and bring him back. Husayn refused to return, relating that Muhammad had ordered him in a dream to move forward irrespective of the consequences. At a place known as Tan'im, he seized a caravan carrying dyeing plants and clothes sent to Yazid by the governor of Yemen. Further on the way, at a place called Tha'labiyya, the small caravan received the news of the execution of Ibn Aqil. At this point, Husayn reportedly considered turning back, but was supposedly persuaded to push forward by Ibn Aqil's brothers, who wanted to avenge his death. Later, at Zubala, Husayn learned of the capture and execution of his messenger Qays ibn Musahir al-Saydawi, whom he had sent from the Hejaz (western Arabia) to Kufa to announce his arrival. He informed his followers of the situation and asked them to leave. Most of the people who had joined him on the way left, while his companions from Mecca decided to stay with him.