632 -- Muhammad dies, sparking the ongoing controversy about his rightful successor, or caliph. Sunnis believe that the Prophet nominated his close friend, Abu Bakr -- father of Aisha, Muhammad's youngest wife -- while the Shia maintain that he appointed his first cousin and son-in-law, Ali.
634 -- Abu Bakr dies after two years of serving as caliph. Another of Muhammad's father-in-laws, Omar Ibn al-Khattab, is named as his successor. He wins stunning military victories over both the Byzantine and Persian empires.
644 -- Omar is assasinated by a Christian slave. Othman Ibn Affan, a scion of Mecca's ruling Umayyad clan, takes over the caliphate.
656 -- Othman is murdered by dissenters from his army. Ali is finally appointed caliph, a role he reluctantly accepts - becoming the fourth so-caled Rightly Guided Caliph. For Shias, however, he holds the title of Imam, or leader -- the first of 12 Imams believed by "Twelver" Shias to be the true successors of Muhammad. Aisha, Muhammed's most outspoken widow, leads a military campaign against him but is defeated at the Battle of the Camel.
657 -- Ali moves the capital from Mecca to Kufa, situated in modern-day Iraq. Muawiya, an Umayyad brother-in-law of Muhammad's, and a cousin of Othman's, confronts Ali for rule of the caliphate but is defeated at the Battle of Siffin. Unable to overcome Ali in battle, he instead manoeuvres him into accepting arbitration -- a move that causes a schism among his followers, with a breakaway faction, known as the Kharijites, now rejecting Ali's rule.
660 -- Muawiya declares himself caliph in Damascus.
661 -- Ali is assassinated by Kharijites in his mosque in Kufa, leaving Muawiya I as the uncontested caliph.
669 -- Hasan Ibn Ali, Muhammad's grandson the second Imam in the Shiite tradition, is poisoned by his wife on orders from Muawiya I. His brother, Hussein Ibn Ali, becomes the third Imam.
680 -- Muawiya I dies, leaving his son Yazid as caliph. When followers of Hussein rise up against Yazid, he sends 4,000 troops to besiege the third Imam at the Battle of Karbala, leading to a massacre that is commemorated by Shia Muslims during the ten day mourning period known as Ashura. This is arguably the theological beginning of Shia tradition and practice.
Dynasties and splits - the next stage
765 -- Jafar al-Sadiq, the sixth Shia Imam, is poisoned and a dispute arises over his sucession. The dispute develops into a fundamental rift within the Shia community, with a breakaway faction known as Ismailis accepting al-Sadiq's eldest son, Ismail, as rightful seventh Imam, while the mainstream Shias (or Twelvers) accepting his younger son, Musa al-Kazim as successor. This creates a historical split within Shiism.
780-974 -- Foundation of the first Shia state, based in the Maghreb, under the Idrisid dynasty.
909-1171 -- Rule of the Fatimid Caliphate, one of the first and most powerful Shia (Ismaili) caliphates that controlled most of North Africa, the Levant and Arabia.
1501-1736 -- Rule of the Safavid dynasty in Persia marks a major turning point in the history of Shia Islam since it marks an end to the relative mutual tolerance between Sunni and Shia since the time of the Mogul conquests. Antagonism and sectarian strife between the two groups becomes increasingly prevalent. Also, during this period, Ismail I, the founder of the Safavid dynasty, initiates a religious policy to recognise Shiism as the official religion of the Safavid Empire. The fact that modern Iran remains an officially Shia state is a direct result of Ismail's actions. His violent enforcement of Shiism exacerbated sectarian tensions in the region.
In the 20th Century
1904-1908 -- Ongoing violent clashes between Sunni and Shia in South Asia, particularly the Uttar Pradesh area of the Indian sub-continent.
1919-1924 -- The Khilafat movement, a pan-Islamic political campaign, is launched by Muslims in British India to protect the Ottoman Empire during the aftermath of World War I. This provided a momentary rapprochement of the Sunni and Shia communities.
1935-1936 -- Iraqi Shiites stage violent uprisings against the minority Sunni government.
1959 -- Mahmud Shaltut, the rector of Al-Azhar University in Cairo, issues a fatwa recognising Shia Islamic law as the fifth school of Islamic law and authorising the teaching of courses in Shia jurisprudence as part of the University's curriculum.
1979 -- Zulifikar Ali Bhutto, Shia president of Pakistan, is excecuted on questionable charges by Sunni fundamentalist General Muhammad Zia al-Huq.
1979 -- Revolution in Iran overthrows the monarchy and establishes a Shia Isalmic Republic under the figure-head of Ayatollah Ruhollah Khomeini.
1980 -- Following the Iran-Iraq war, persecution and violence against the Shia majority in Iraq becomes increasingly prevalent. Celebration of Shia festivals, such as the Ashura, is banned under Saddam Hussein's Baath governmet.
1991 -- Shia Muslims perpetrate a series of uprisings in southern and northern Iraq, which are ruthlessly and systematically crushed by Saddam's ruling Baath party. 50-100,000 people are allegedly killed, and thousands more forced to flee their homes.
1996 -- More than 200 people are killed in northern Pakistan during a shootout between Sunni and Shia factions.
2000 -- Hassan Nasrallah, leader of the Lebanese Shia militia Hizballah, negotiates with Israeli prime minister, Ehud Barak, to end the Israeli occupaton of southern Lebanon.
2005 -- Iraqi parliamentary elections brings in a Shia majority government for the first time since the 2003 invasion.
2005 -- Anti-Shia insurgents led by Jordanian-born Raed Mansour al-Banna kill 127 people in Al Hillah, Iraq. Following the attack, Shia mobs attacked the Jordanian embassy in Baghad, causing ambassadors to be withdrawn from both countries.
2007 -- The sectarian violence in Iraq following the 2003 American-led invasion escalates to a level described by the United States national Intelligence Estimate as "civil war". At least 2.7 million people are estimated to have been displaced by inter-faction hostility.