From Karbala to Iran: How Shia Islam has evolved across centuries

From the dispute over Ali's succession to the legacy of Karbala, here is how Shia Islam evolved, what its core beliefs are, and where Shia communities are found today

Shias, or Shi’a Muslims, are the second-largest branch of Islam after Sunnis. The term Shia comes from Shi’at Ali, or the “party of Ali”, and refers to Muslims who believe that the leadership of the community after Prophet Muhammad should have passed to Ali ibn Abi Talib, the Prophet’s cousin and son-in-law, and then through his family line. Shias and Sunnis have several differences, yet their core beliefs remain the same. As conflict in West Asia rages on, here is a closer look at how Shias shape the Muslim world.

 

How did the Shia-Sunni split begin?

 

Islam was founded in the early seventh century. The Shia-Sunni split began after Prophet Muhammad died in 632 CE. The divide had its roots in the question of succession, which did not exist because Prophet Muhammad died without naming a successor. One group believed leadership should remain within the Prophet’s family and supported Ali ibn Abi Talib as the leader of the Islamic community. Others supported Abu Bakr as the first caliph. The followers of Ali came to be known as Shias and those who supported Abu Bakr became Sunnis. 

 

The next few decades were marked by disputes over legitimacy, authority and religious leadership. The defining moment for Shias came in 680 CE, when Hussein ibn Ali, the Prophet’s grandson, and his family were killed at the Battle of Karbala. For Shias, Karbala symbolises sacrifice, injustice and resistance to illegitimate rule. Ashura is observed on the 10th day of Muharram and marks Hussein’s martyrdom, remaining one of the most important occasions in the Shia religious calendar.

 

What do Shia Muslims believe?

 

Shias are estimated to account for about 10 to 13 per cent of Muslims worldwide. At the core of Shia belief is the idea of Imamate. Shias believe that the leadership of the Muslim community after Prophet Muhammad rightfully belonged to Ali ibn Abi Talib and then to his descendants through the Prophet’s family, the Ahl al-Bayt.

 

The largest Shia sect, Twelver Shi’ism, considers Imams not just political heirs but divinely guided authorities who preserve the true interpretation of Islam. Despite these distinctions, Shias share Islam’s central foundations with Sunnis: belief in one God, the Quran, Prophet Muhammad, prayer, fasting, charity and pilgrimage.

 

How does Shia Islam differ from Sunni Islam?

 

Sunnis historically accepted leadership through political selection or community consensus. Shias, by contrast, held that rightful authority belonged to Ali and his descendants. Over time, this produced differences in legal traditions, distinct hadith collections and some variations in ritual practice and religious commemoration.

 

This difference is also reflected in religious authority. Twelver Shi’ism developed a stronger clerical structure than Sunni Islam. Senior scholars in Twelver Shi’ism hold titles such as Ayatollah and Grand Ayatollah, and sometimes serve as maraji, or sources of emulation, whose legal opinions followers may adopt. Sunni Islam also has a deep scholarly tradition, but religious authority is generally more decentralised and local.

 

What are the main Shia sects?

 

Twelver Shias, also called Ithna’ashari Shias, are the largest branch of Shia Islam. They believe that Prophet Muhammad’s rightful successors were 12 Imams from the line of Ali ibn Abi Talib. Their distinctive belief is that the 12th Imam did not die but went into occultation and will return in the future as the Mahdi. Twelvers form the dominant Shia community in Iran and Iraq and are also found in countries such as Azerbaijan, Bahrain, Lebanon, India and Pakistan.

 

After the death of Imam Jafar al-Sadiq, divisions within the early Shia community led to the emergence of the second major branch, the Ismailis. Today, Ismaili communities are present across Asia, West Asia, Africa, Europe and North America. India and Pakistan have long-established Ismaili populations. Nizari Ismailis are the largest branch and are globally dispersed, while Musta’li Ismailis, including the Bohras, are concentrated mainly in western India.

 

Zaydis are another branch of Shia Islam found mainly in Yemen. They follow Zayd ibn Ali and believe that a leader should be a learned and capable descendant of the Prophet’s family who is willing to stand against unjust rule. Unlike Twelver Shias, they do not believe in a hidden Imam or attribute infallibility to the Imam. In some legal traditions, Zaydi practice is often seen as closer to Sunni Islam than Twelver Shi’ism.

 

Where are Shia Muslims found today?

 

Twelver Shias are concentrated mainly in Iran, Iraq and Azerbaijan, while Bahrain, Saudi Arabia and Kuwait also have sizeable Twelver communities. Yemen remains the main centre of Zaydi Shias.

 

In South Asia, India and Pakistan have large Shia populations belonging to both Twelver and Ismaili traditions. Tajikistan is an important Ismaili centre, while East Africa remains a major hub for Ismaili communities. In Europe, North America and other Western countries, Shia populations are largely found in diaspora communities made up mainly of Twelvers and Ismailis.

 

What is the presence of Shia Muslims in India?

 

In India, Shias are a minority within the Muslim population and are found mainly in Uttar Pradesh, Jammu and Kashmir, Hyderabad and parts of western India. The largest group is Twelver Shias, but India is also home to important Ismaili communities, especially Nizari Khojas and Musta’li Bohras.

 

The Institute of Ismaili Studies identifies India as a major centre for both Nizari and Bohra Ismaili traditions. Ayatollah Ali Khamenei’s link to India is mainly religious. Iran maintains a representative of the Supreme Leader in India.

 

Why does Iran matter in the Shia world?

 

Ever since the Islamic Revolution of 1979 in Iran, the country has been widely seen as the political centre of Shia Islam. Iran amended its constitution to give sweeping powers to the head of state, who is a Shia cleric.

 

In simple terms, a senior cleric holds crucial decision-making powers in Iran. Since nearly 95 per cent of Iranians are Shias, the country does hold influence over sections of the global Shia population.

 

However, the Shia religious system is highly decentralised. A Shia believer in South Asia may follow a Grand Ayatollah based in Iran, but this does not necessarily shape the person’s political views. Therefore, the religious authority of Iran’s Supreme Leader is not universal across the Shia world and is not comparable to the pope in Christianity.

 

The bottom line

 

Put simply, Shias are Muslims who believe leadership after Prophet Muhammad should have remained with Ali and the Prophet’s family. Their faith gives special importance to the Imams, and their religious identity is deeply shaped by the memory of Karbala.

 

Like Sunnis, they share the basic beliefs of Islam but differ on questions of religious authority, historical interpretation and some practices. Iran is the most prominent Shia-majority country, yet Shias are spread across many regions and represent a diverse global community.