This paper traces the origins of the Shia-Sunni denominational split in Islam, beginning with the succession dispute following Prophet Muhammad's death in 632 CE and the subsequent theological and political divergences that created two distinct Islamic traditions. The paper then analyzes how this centuries-old religious conflict has directly affected U.S. national security through regional power struggles, sectarian violence, geopolitical interventions, and conflicts including the Iran-Iraq War, the 2003 Iraq invasion, and the rise of the Islamic State. By examining key historical events—from the 1953 CIA-backed coup in Iran to the Iraqi insurgency and Syrian civil war—the paper demonstrates that understanding the Shia-Sunni dynamic is essential for comprehending Middle Eastern instability and U.S. military and diplomatic strategy in the region.
Many religions have different denominations, and Islam is not an exception in this regard. The two primary denominations of Islam are Sunni Islam and Shia Islam. The majority of Muslims across the globe are Sunni, estimated to be roughly 85–90% of the Muslim population, while the remaining smaller number of Muslims—approximately 15%—are Shia.
Further demarcations indicate that most Shias belong to the tradition known as Twelver, with the rest of the Shia identifying with other traditions. Twelver refers to the number of descendants of Muhammad that this sect of the Shia recognize. Another group is referred to as the Seveners, since they recognize only seven descendants who were official caliphs of Islam.
This theological distinction is further complicated by the concept of Occultation, which refers to a messianic figure, or Mahdi, who is born but goes into hiding (referred to as disappearing) in order to be safe. The Mahdi concept has been criticized as a pious fraud which promotes the idea of waiting faithfully for a messiah who will renovate the world by eradicating evil and restoring full good. Moreover, a period of Occultation permits an elaborate system of communication between believers and agents of the Mahdi who has disappeared, as only certain privileged individuals can conduct the sacred duty of contacting the Mahdi on behalf of the believers. In this scenario, the Mahdi is said to be physically present but in hiding. In other scenarios, no one presides over the Shia faithful, who all await the Mahdi. An objective scholar can see the possibilities for controlling situations and believers without authentic authority to do so.
In any given Muslim community, Sunnis tend to be in the majority. This is true for Muslim communities in most of the Arab world and in Africa, China, South Asia, and Southeast Asia. Globally, the largest number of practicing adherents of the Sunni tradition reside in Indonesia. The Shia, on the other hand, are in the majority of Muslim populations in Azerbaijan, Bahrain, Lebanon, Iran, and Iraq. The largest population of Shia Muslims are in Iran. Pakistan is uniquely positioned as the country with both the second-largest Sunni population and the second-largest Shia Muslim population in the world.
The death of a religious leader is a vulnerable time for believers and for the religion as an entity. When Muhammad, the prophet of Islam, died in 632, the response of believers was chaotic as a caliph for all of Islam had not been identified to become the successor to Muhammad. That Muhammad was a prophet, possessing special knowledge about the Quran and professing communion with God (Allah), made Muhammad fundamentally irreplaceable. Muslim believers stood on a precipice as it became clear that their beloved Muhammad was dying.
Muslim elders in Medina agreed to designate Abu Bakr as caliph, thereby addressing the urgent need for selecting a successor to Muhammad. Abu Bakr was the father-in-law of the prophet Muhammad. By selecting Abu Bakr, the elders established a precedent that caliphs who were successors of Muhammad would be members of the Quraysh tribe. However, a minority of the elders favored a man named Ali, calling themselves Shiat Ali, or the partisans of Ali. In 656, following the assassination of his predecessor, Ali became the fourth caliph; there is subsequent rebellion against him among some Muslims.
A growing dispute escalated into the Battle of Siffin, a conflict pivotal to the shift from argument and disagreement to full-scale violence. What soon followed was the even larger Battle of Karbala in 680, in which Hussein ibn Ali, the son of Ali, marched against the caliph's army in Iraq. Hussein's army was massacred, and he and his entire household were killed at the hands of the Umayyad Caliph Yazid I. The divide between the Shiites and the Sunnis deepened.
What began as an ideological schism and a scramble for power deteriorated into revenge seeking and an irreparable breach between the Sunni and the Shia. As the two denominations continued to mature separately from one another, differences in beliefs, customs, traditions, and religious practices emerged. While all Muslim groups believe the Quran is divine, issues about jurisprudence and the hadith have created strong separations among the denominations of Islam. Hadith is the process of attribution that accompanies secondary interpretations of a divine book, which necessarily follows as believers strive to align what they understand of the Quran with what they know Muhammad said, and what they believe he said, tacitly approved, or sanctioned.
Over many hundreds of years, the relations between the Sunni and the Shia have been characteristically cooperative or hostile, depending on substantive political events in Muslim countries. Sectarian violence—a term for the conflict and strife inspired by differences in ideology or religion associated with different sects within a larger community or nation—is particularly apt for describing the conflict that persists between Sunni and Shia throughout the Middle East. A series of epic power struggles and international conflicts have intensified sectarian violence among Islamic sects.
Prior to World War I, the Shiite clerics practiced a time of Quietism in which they tolerated the rule of monarchs as long as religious law was not violated and as long as the Shiite community was preserved and protected. A perfect Islamic state was considered pie-in-the-sky. In the 1920s, both Shiite and Sunni Arabs revolted against British control of Iraq, and shortly after, Kemal Ataturk abolished the Ottoman sultanate along with the Turkish Sunni caliphate. Still, the Shiite clerics held the line until 1925, when Reza Pahlavi, a Persian military officer, conducted a coup, seized power, and declared himself shah. Persia officially became Iran, and a secular government was established, which essentially shut out the Shiite clergy.
After Pahlavi developed relations with Nazi Germany during much of the 1930s, he sufficiently burned bridges with the Allies, such that early in World War II, Britain and the Soviet Union seized part of Iran and made the shah abdicate the throne. Shortly before World War II, in 1932, Iraq became an independent nation governed by King Faisal, who was a Sunni Arab. By 1941, British and Soviet military forces had occupied Iran. A joint CIA and British intelligence operation in Iran worked to keep the shah on the throne and in power by ousting nationalist Prime Minister Mohammad Mossadegh.
By 1953, the political instability in Iran forced the new shah to flee, until a cooperative coup devised by the CIA and the British returned him to power. Those experiences caused considerable distrust, and the shah established a body of secret police that mercilessly destroyed anyone who challenged his rule. However, the shah's long arm did not extend to the mosques, which provided a venue and cover for dissidents, including Ayatollah Ruhollah Khomeini. As an instigator of widespread protests and unrest in Iran, the Ayatollah was arrested and exiled to Najaf in Iraq in 1963.
His exile provided time and space for the Ayatollah to conceptualize a Shite Islamic state that would be controlled by the clergy. The Ayatollah's rationale was that only clerics had true knowledge of Islamic law and so were the only people qualified to be the political leaders of the state. A primary reason why this new concept of religious government did not have quick uptake by the Shiite clerics in Iraq, Iran, and Lebanon was widespread acceptance of the eventual return of the Twelfth Imam (the hidden Imam of the 9th century) when God determined it was time to bring justice to earth.
In 1978, the cities in Iran were overrun by protesters calling for the overthrow of the shah. A full-blown revolution followed that was characterized by a roiling conflation of ideologies: anti-imperialism, communism, secular pluralism, and a supreme religious leader for the new Islamic state. The Shiites were emboldened by their accomplishments and tilted ever more toward activism—a characteristic that is still in evidence. Khomeini sought a unified revolution with the Sunnis fully onboard. However, many Sunni activists rejected the Iranian revolution out of hand, and Sunni governments began to respond more aggressively. Indeed, the Saudis began to strengthen Sunni fundamentalist movements.
Saddam Hussein went into a full aggressive state in 1980 with the invasion of Iran, a move intended to overtake the Iranian oil fields. In 1990, Saddam set his sights on Kuwait oil fields, which brought the U.S. military into the fray in 1991 to drive the Iraqi army from Kuwait. That same year saw the Shiites of southern Iraq stage their own rebellion against Saddam, but they were brutally crushed with thousands of Shiites killed by Saddam's military.
Economic sanctions were placed on Iraq from 1991 through 2003 due to suspicions of nuclear development within the country, which further prompted U.N. weapons inspectors to move to destroy biological, chemical, and nuclear weapons in Iraq. In 2001, the Sunni Muslim fundamentalist group known as Al-Qaeda conducted several attacks on the U.S. mainland, killing 3,000 people. In response, the U.S. military invaded Afghanistan to oust the Sunni Taliban government. The U.S. military invaded Iraq in 2003, bringing down Saddam. This was followed in 2005–2006 by the eruption of an Iraqi insurgency, which was led by Al-Qaeda and Sunni Baathists.
Iran saw the election of hard-line fundamentalist Mahmoud Ahmadinejad as president in 2005 and began pursuing in earnest the acquisition of nuclear technology for Iran. The U.N. Security Council imposed economic sanctions on Iran again in 2006 following the further development of nuclear activities. In 2007, more U.S. troops were sent to Iraq. Since that time, the tension between the Sunni and Shiite communities has intensified during power struggles.
Conditions in Bahrain were dismal for years with citizens experiencing human rights violations and extensive, systematic preferential treatment of Sunnis. The Bahraini protests were a series of uprisings—some would call it a revolution—intended to achieve greater equality and political freedom for the majority Shiite population in Bahrain.
"Contemporary sectarian displacement and security implications in post-ISIS Iraq"
Today in Iraq, the Shiite military have taken over villages that were once the homes of Sunni residents, especially in locations where Sunni homes were situated on roads traveled by Shiites on their way to sacred sites, such as the Shiite shrine of Imam al-Askari in Samarra, north of Baghdad. The village of Balad has many shrines dedicated to imams that are revered by Shiites, and the country along the Tigris River is peppered with Sunni villages and towns. The distrust of Sunnis by the Shiites is reminiscent of the cruel treatment of French people who stayed in their homes when the Germans took over and took up residents. Women were shorn to shame them for cavorting with or supplying food and shelter to the enemy, even though there was general recognition that they did not have a choice.
The same prejudicial story is playing out for the Sunnis, many of whom tried to stay in their homes and plow their fields while the Islamic State overran their villages. Many Sunni chose to flee their homes, abandoning their only belongings and livelihoods, keeping just ahead of the violent wave of Islamic State forces. The Shiite military are reclaiming the Sunni land as originally their own, and they have closed ranks. Even though Grand Ayatollah Ali al-Sistani admonished the Shiites for their rejection and threats against the Sunni and condemned the violent militiamen, saying in a fatwa (edict) that they were to stop stealing Sunni-owned property in the wake of the Islamic State retreat, sectarian revenge persists.
American, Kurdish, and Iraqi forces are driving out the Islamic State (ISIS, ISIL) and have hopes of eliminating it from Iraq altogether within one to two years. Yet the Shiite and Sunni communities impacted by these forces remember all too well the 2006–2008 civil war and the 2010–2014 violence against the Sunnis, followed by the apparent acceptance of the Islamic State by the Sunni. As the Shiite military moves further into Sunni land to force out ISIS (ISIL), Sunni villagers and farmers fear for their lives. The problem this holds for the U.S. and the Iraqi army is that the Sunnis may align with the Islamic State as the perceived lesser of two evils.
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