The new US-led war against the Islamic State in Iraq and Syria (ISIS) is packaged as part of the war against barbaric terrorism. British Prime Minister David Cameron epitomized that mindset when he described ISIS fighters as “monsters.” ISIS’s behavior undoubtedly lends credibility to that description. Especially the graphic videos showing the beheadings of two American journalists and a British humanitarian aid worker have understandably led to revulsion throughout the West and galvanized a determination to retaliate. At times, ISIS members behave like typecast villains out of a bad Hollywood movie, validating the narrative of pro-war advocates in the United States and other countries.

But if Washington and its Western allies succumb to the illusion that the group is nothing more than a vicious terrorist organization, they will miss the crucial larger context and get drawn into a complex Middle Eastern power struggle. Such a blunder would likely lead to a frustrating, long-term, and ultimately unwinnable military crusade. Although angry Westerners may be reluctant to concede the point, ISIS is a lot more than just about ISIS.

Even the organization’s spectacular brutality is hardly unique in the region. ISIS is fond of beheading opponents, but a key member of the coalition that Washington is assembling to combat the group has routinely displayed similar barbarity. In 2014 alone, Saudi Arabia has executed 46 people through beheadings — nearly half of them for nonviolent offenses. Likewise, ISIS is not the only faction to slaughter military prisoners. At nearly the same time that videos surfaced of ISIS’s execution of captured Iraqi government troops, Shiite militias fighting alongside Baghdad’s forces committed comparable atrocities against Sunni captives on at least two occasions.

Indeed, the emergence of ISIS is merely the latest episode in an exceptionally nasty Sunni-Shiite struggle for preeminence throughout the Middle East. That is why treating the group as just a rogue terrorist operation would be a major policy blunder. ISIS arose from two sources, both of which reflect the wider sectarian conflict.

The primary source was the civil war in Syria between largely Sunni insurgents and Bashar al-Assad’s governing coalition of Alawites (a Shiite offshoot), Christians, and other religious minorities who are petrified about possible Sunni domination. Saudi Arabia, Qatar, and Turkey enthusiastically backed the insurgents, while the United States provided some aid to them as well. Many of those rebels, though, subsequently formed the core of ISIS.

The secondary source of ISIS’s rise was the continuing sectarian animosity in Iraq. Eliminating Saddam Hussein’s rule ended decades of Sunni domination of that country’s politics and economy. The new Shiite-led government was in no mood for conciliating the displaced elite that had stifled their faction for so long. Instead, that regime, led by Prime Minister Nouri al-Maliki, seemed to go out of its way to marginalize and humiliate the Sunni minority. Iraq has seethed for years because of that sectarian hatred, drifting to the brink of civil war in 2006 and 2007, and finally exploding into a full-blown internecine conflict this year. Some Iraqi Sunnis may harbor worries about ISIS’s extremism, but they also see the group as the one entity capable of mounting a serious armed challenge to the Baghdad government.

It is imperative for the Western powers to comprehend that ISIS is a product of a larger sectarian feud. If they wish to pursue a war against ISIS, they must confront some troubling realities. First, they will have to accept the need to embrace strange and perhaps unpalatable allies. Among ISIS’s most vehement opponents are Assad’s government, Iran (the region’s leading Shiite power), and Tehran’s proxy in Lebanon, Hezbollah. Washington and its NATO allies may indulge in the illusion that weakening ISIS will not benefit Assad, the Iranian mullahs, and Hezbollah, but it is an illusion. Western governments need to make some hard choices and set priorities, if they wish to proceed with the crusade against ISIS.

Another troubling reality is that some other members of the coalition are likely to be extremely unreliable. That is especially true of Turkey and Saudi Arabia. Indeed, Ankara seems to be little more than a paper member of the coalition, since it has already refused to take part in any military action against ISIS and has barred the United States from using bases in Turkey to launch air strikes. It is not even clear that the Erdoğan government will try to seal the border with Syria to thwart new recruits from joining ISIS. Ankara may not be happy about ISIS’s radicalism, but as a Sunni power, Turkey is not about to wage war against the group and strengthen the position of Iran and other Shiite players.

Saudi Arabia’s prospective behavior is an even greater cause for concern. Indeed, Riyadh’s actions in Iraq, and especially in Syria, were a major factor in ISIS’s rise to prominence in the first place. Saudi aid to Syrian rebels helped empower radical factions. That was hardly surprising, given the Saudi government’s long-standing promotion of the extremist Wahhabi strain of Islam. Saudi leaders may now realize that they helped create a Frankenstein’s monster, but Washington’s belief that Riyadh, as a member of the anti-ISIS coalition, will work to strengthen “moderates” in Syria and elsewhere is extraordinarily naïve. The Saudi government will more likely try to back hard-line Sunni elements that, perhaps for sufficient financial inducements, are willing to break with ISIS and take guidance from Saudi patrons. Although Riyadh may want to marginalize ISIS, there is no desire to crush the organization and see the power of Tehran and its Shiite allies in Iraq, Syria, and Lebanon grow.

Without understanding that complex context, the United States and the other Western powers are wandering into a geopolitical minefield. Defeating ISIS, even in a narrow military sense, may prove quite difficult. Avoiding entrapment in the larger Sunni-Shiite regional struggle for dominance is likely to prove impossible. Western leaders need to ask themselves if the current strategy is wise, or whether it would be more sensible to take a step back and let the underlying sectarian conflict play out. True, ISIS might ultimately attack targets in the West, but intensified US-NATO intervention in the Middle East is likely to increase, not decrease, that risk. There is scant evidence, though, that Western officials have thought through the implications of the policy they are adopting. They need to do so without delay.