Sectarian violence among Muslims
Sectarian violence among Muslims has been noted from the time of the first century of Islam to the present day.
Following the 2003 Invasion of Iraq and subsequent fall of Saddam Hussein's regime, the minority Sunni sect, which had previously enjoyed increased benefits under Saddam's rule, now found itself out of power as the Shia majority, suppressed under Saddam, sought to establish power. Such sectarian tensions resulted in a violent insurgency waged by different Sunni and Shia militant groups, such as al-Qaeda in Iraq and the Mahdi Army. Following the U.S. withdrawal in 2011, violence has increased to 2008 levels. In February 2006, more than 100 people were killed across Iraq, when violence between the two Muslim rival sects erupted. It has left over a hundred people dead and dozens of mosques and homes destroyed. 
In Saudi Arabia
The Grand Mufti of Saudi Arabia, Abdul-Aziz ibn Abdullah Al Shaykh, issued a fatwa on 12 September 2013 that suicide bombings are "great crimes" and bombers are "criminals who rush themselves to hell by their actions". Sheikh described suicide bombers as "robbed of their minds... who have been used (as tools) to destroy themselves and societies."
On 16 September 2013 he condemned violence against non-Muslims living in Islamic countries or Muslims labeled as infidels. The Grand Mufti condemned acts that cause the "shedding of blood of Muslims and of those living in their counties in peace." Sheikh Al Shaykh stated, "Given the dangerous developments in the Muslim world, I would like to warn against the danger of attacking Muslims and those (non-Muslims) under Muslim protection."
"In view of the fast-moving dangerous developments in the Islamic world, it is very distressing to see the tendencies of permitting or underestimating the shedding of blood of Muslims and those under protection in their countries. The sectarian or ignorant utterances made by some of these people would benefit none other than the greedy, vindictive and envious people. Hence, we would like to draw attention to the seriousness of the attacks on Muslims or those who live under their protection or under a pact with them," Sheikh Al-AsShaikh said, quoting a number of verses from the Qur'an and Hadith.
Ahlu Sunna Waljama'a is a Somali paramilitary group consisting of Sufis and moderates opposed to the radical islamist group Al-Shabaab. They are fighting to prevent Wahhabism from being imposed on Somalia and protecting the country's Sunni-Sufi traditions and generally moderate religious views.
Bahrain is ruled by the Al Khalifa family, who are part of the Sunni minority since 1783. Bahrain's Shia majority has often complained of receiving poor treatment in employment, housing, and infrastructure, while Sunnis have preferential status. The Bahraini government has reportedly imported Sunnis from Pakistan and Syria in an attempt to increase the Sunni percentage.  Shiite Muslims are blocked from serving in important political and military posts. Sunnis and Shia often stress that, no matter what their denomination, they are all Bahrainis first and foremost. However, sectarianism seethes below the surface of society.
Minor sectarian clashes have occurred during the Bahraini uprising. On 4 March 2011, about six people were injured in Hamad Town and police intervened to disperse young Shi'ites and largely recently naturalised Sunni Arabs who clashed with knives, sticks and swords, witnesses said. It is unclear what caused the incident, with both sides blaming the other for the outbreak of violence. This incident marks the first sectarian violence since protests erupted on 14 February. A spokesman for Al Wefaq opposition party said the clashes were due to a dispute between families in the area and weren't sectarian. Others said that Shiite youth had targeted naturalised Sunnis living in the area.
- Islamic schools and branches
- Sectarian violence
- Sectarian violence among Christians
- Persecution of Ahmadis
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- McTernan, Oliver J. 2003. Violence in God's name: religion in an age of conflict. Orbis Books.
- Middle East sectarianism explained: the narcissism of small differences Victor Argo 13 Apr 2015 Your Middle East