Shia Islam in Iraq () has a history going back to the times of Ali ibn Abi Talib, the first imam of Shia Islam and fourth caliph of Sunni Islam who moved the capital of the early caliphate from Medina to Kufa (or Najaf) two decades after the death of Muhammad. Today, Shia Muslims make up the majority of the Iraqi population. Iraq is the location of the holy cities of Najaf and Karbala, pilgrimage sites for millions of Shia Muslims. Najaf is the site of Ali's tomb, and Karbala is the site of the tomb of Muhammad's grandson, third Shia imam Husayn ibn Ali. Najaf is also a center of Shia learning and seminaries. Two other holy sites for Twelver Shia in Iraq are the Al-Kadhimiya Mosque in Baghdad, which contains the tombs of the seventh and ninth Shia Imams (Mūsā al-Kādhim and Muhammad al-Taqī) and the Al-Askari Mosque in Sāmarrā, which contains the tombs of the tenth and eleventh Shia Imams (Ali al-Hadi and Hasan al-‘Askarī).
After the U.S.-led invasion in 2003, there has been widespread sectarian violence between Shias and Sunnis in Iraq, which became high-intensity in the wars in 2006–2008 and 2013–2017, which involved the Islamic State terror group.
History
7th to 10th centuries
After being named caliph in 657, Imam Ali ibn Abi Talib established his capital at Kufa in present-day Iraq. The Battle of Karbala took place in 680, where Husayn ibn Ali was martyred by Umayyad forces of Ubayd Allah ibn Ziyad and Umar ibn Sa'd at the orders of Yazid ibn Mu'awiya. Following the horrific event, many called for Husayn's vengeance. Sulayman ibn Surad led the Tawwabin uprising in January 685, but was defeated and killed in Battle of Ayn al-Warda. After the failed uprising, Mukhtar al-Thaqafi once again called for the establishment of an Alid caliphate and for retaliation for Husayn's killing, and took over Kufa in October 685. Aided by Ibrahim ibn al-Ashtar, they successfully drove the Umayyads out of Kufa and defeated them in several battles, including the Battle of Khazir in 686, but were defeated shortly afterwards in 687, when Kufa was besieged by the governor of Basra Mus'ab ibn al-Zubayr.
In the early Islamic period, Kufa effectively became the "second capital" of Shiism after Medina, the residence of the Twelve Imams, and acted as a source of many Shiite scholars and disciples of the Twelve Imams, including: Hisham ibn al-Hakam, Zurarah ibn A'yun, Burayd ibn Mu'awiya, Mu'min al-Taq, Aban ibn Taghlib, Abu Basir al-Asadi and Muhammad bin Muslim, all disciples of Imam Ja'far al-Sadiq (702–765 CE). It was in Kufa where Zayd ibn Ali, the principal figure of Zaydism, led an uprising against the Umayyad rule of Hisham ibn Abd al-Malik which ended with Zayd's execution and burning, while Basra witnessed the Alid revolt of 762–763 by Muhammad al-Nafs al-Zakiyya's brother Ibrahim, who was said to have amassed a force as large as 100,000. Moreover, the 7th Twelver Imam Musa al-Kazim was repeatedly imprisoned in Baghdad and Basra at the orders of Abbasid caliphs al-Mansur, al-Hadi, al-Mahdi and Harun al-Rashid. During Al-Ma'mun's reign, in a sudden departure of anti-Shia policy, Imam Ali al-Rida was designated heir apparent of al-Ma'mun, but was later poisoned by al-Ma'mun himself. Some Shia officials managed to gain influence in the Abbasid court, such as Ali ibn Yaqteen, a Kufan who became a minister of the Abbasid caliph with the approval of Imam Musa al-Kadhim to assist the Shia.
Aside from mainstream Shia Islam, Iraq was also the hotbed of many extinct Shia sects which temporarily flourished. Kufan followers of Mukhtar al-Thaqafi later formed the Kaysanite sect, who traced the line of Imamate to Muhammad ibn al-Hanafiyya. The Kaysanites had a significant role in the Abbasid Revolution after they managed to rally Shia support in Iraq for the uprising against the Umayyads. However, after the revolution, most Kaysanites soon joined Ja'far al-Sadiq or Muhammad al-Nafs al-Zakiyya, and eventually Ja'far al-Sadiq after the demise of Muhammad. Another extinct sect are the Qarmatians, a sect of Isma'ili Shias founded by the Iraqi-born Hamdan Qarmat. Hamdan assumed the leadership of Isma'ili missionary activity in the rural environs () of Kufa and southern Iraq, and Qarmatian creed soon flourished in southern Iraq. Among the Iraqi s trained and sent to missions by Hamdan and Abu Muhammad were Ibn Hawshab (to the Yemen), and Abu Abdallah al-Shi'i, a Kufan-born dā'ī who later helped convert the Kutama in Ifriqiya and opened the way to the establishment of the Fatimid Caliphate.