In the West, Islam is often seen as a single, monolithic faith. However, the Muslim faith has a major schism between Sunni and Shia Muslims.
Sunni and Shia Muslims have been separate since the year 632, when the death of the prophet Mohammed sparked a conflict of succession.
His position as religious leader was passed on to Abu Bakr as-Siddiq, a close companion to Mohammed. Others in the community felt that the position belonged to Ali ibn Abi Talib, the cousin of Mohammed, instead.
Those who supported Abu became known as Sunnis, while those who supported ibn Ali became Shi’ites.
To this day, Shi’ites believe the position of caliph belongs to direct descendants of Ali, while Sunnis believe that the caliph should be elected by leaders of the Muslim community.
The geographical division of Sunni and Shia Muslims
Only around 10-13% of the world’s Muslim population are Shias, as the Pew Research center reports, while the rest are Sunnis. However, the Shia population is geographically concentrated in Iran, Iraq, and Palestine.
The geographic concentration is also the main source of tension, however, according to Georgetown University Center for Muslim-Christian Understanding.
For most of their history, Sunni and Shia Muslims tolerated each other, and there were no large-scale conflicts.
In fact, that only started occuring in the 1970s, intensifying with the radical Iranian Revolution, as well as the Afghan War. The religious conflict became a smoke screen for inter-state rivalry and the uprising against the socio-economic status of Shia muslims in Sunni countries.
As explained in a paper by the Brookings Institution, even greater sectarian tensions have been ignited this decade, both because of the Iraq and Afghan Wars, and with the Shia-Sunni divide being drawn up as another battle line in the Arab uprising.
In Iraq, Islamic State militants are also exploiting tensions between Sunni and Shia Muslims in their quest to create an Islamist caliphate.