The Sunni and Shia Divide: A Significant Factor in Middle Eastern Tensions
The assertion that the Sunni-Shia divide was the most important cause of religious tensions in the Middle East from 1908 to 2011 is a complex one, requiring nuanced analysis. While the historic schism undoubtedly played a significant role, other religious tensions, particularly those linked to the Israeli-Palestinian conflict and the rise of Islamic fundamentalism, also contributed significantly to the region's instability.

The Enduring Impact of the Sunni-Shia Divide
The roots of the Sunni-Shia split lie in the seventh century, stemming from disagreements over the rightful successor to the Prophet Muhammad. This historical divide continued to influence religious and political dynamics throughout the 20th and 21st centuries. In Iraq, for example, the dominance of the Sunni Ba'athist regime under Saddam Hussein fueled resentment among the Shia majority. This resentment was amplified by the regime's suppression of Shia religious practices and institutions, culminating in the Shia uprising of 1991. The US-led invasion of Iraq in 2003, while initially aimed at removing Saddam, inadvertently exacerbated the Sunni-Shia tensions, leading to a brutal civil war that destabilized the nation.

Syria, another key example, witnessed the rise of the Alawite minority sect, closely aligned with Shia Islam, to power. Under the Ba'athist regime of Hafez al-Assad and his son Bashar al-Assad, the Alawite regime's grip on power fueled sectarian tensions with the Sunni majority. These tensions boiled over in the Syrian Civil War in 2011, as Sunni groups, including the Islamic State, sought to overthrow the regime. The conflict further exacerbated the Sunni-Shia divide, drawing in regional and international players such as Iran and Saudi Arabia, who supported opposing factions.

Beyond the Sunni-Shia Divide
While the Sunni-Shia divide had a significant impact on the Middle East, it is inaccurate to claim it was the sole or most important cause of religious tensions. Other religious divisions and conflicts deserve equal consideration. The conflict between Jews and Muslims, fueled by competing claims over Jerusalem and the Palestinian territories, has been a major source of instability since the early 20th century. This tension reached its peak with the first and second Intifadas in 1987 and 2000, respectively, and continues to be a major obstacle to peace in the region.

The rise of Islamic fundamentalism, particularly the Iranian Revolution in 1979, also contributed to religious tensions in the Middle East. The Islamic Republic of Iran, under the leadership of Ayatollah Khomeini, sought to export its Islamic revolution, supporting Shia groups in other countries and challenging US influence in the region. This led to increased friction with Sunni-dominated Gulf states, such as Saudi Arabia, and the creation of a complex web of allegiances and rivalries. Furthermore, the emergence of radical Islamist groups like al-Qaeda and ISIL, while not solely motivated by the Sunni-Shia conflict, further inflamed sectarian tensions and contributed to instability across the Middle East.

Conclusion
In conclusion, the Sunni-Shia divide was a significant factor in the religious tensions of the Middle East from 1908 to 2011. However, it was not the only factor, and its importance can be debated. Other religious divisions, such as the Israeli-Palestinian conflict and the rise of Islamic fundamentalism, also played crucial roles in shaping the region's political landscape and generating instability. To fully understand the complex tapestry of religious tensions in the Middle East, a comprehensive analysis of all these factors is necessary.