While President Obama is correct in saying the war on terror is not and mustn’t become a war against Islam, it would be foolish to ignore the religious dimension of Islamic terrorism as now reflected in the Holy Week attacks in Brussels. To do that would risk making the secularist worldview underlying the strategic thinking of many Western commentators and policy types an obstacle to understanding the present crisis.

But what is the role of religion here? There is a partial answer in a statement by the Islamic State celebrating the attacks in Paris late last year and calling France “the lead carrier of the cross in Europe.” Secularist France, with an official policy of “laicite” (extreme church-state separation), a “carrier of the cross”? ISIS appears unaware that times have changed since the days of the Crusades.

Two religious realities stand out when looking at today’s Middle East.

One is that much of what happens there is rooted in a power struggle between two great branches of Islam, the Sunnis and the Shiites. (Iran is Shiite, Saudi Arabia is Sunni.) The other is that adherents of fundamentalist groups like ISIS, al-Qaeda and the rest share the conviction that violence is an acceptable tool for advancing its version of Islam against non-Muslims and its Islamic foes.

Absent a grasp of these religious realities, there is a worrisome possibility that the U.S. and its allies will fumble the ball by taking into account only the political and military aspects of the situation. Nothing in the 2016 presidential campaign so far gives much reason for supposing that won’t happen.

It wasn’t always so. When the West in earlier times faced a serious threat of a military nature from Islam, it responded — successfully — by invoking its own faith commitment. The battles of Lepanto (1571) and Vienna (1683) are dramatic illustrations.

At Lepanto the ships of a Holy League organized by Pope St. Pius V and consisting of Genoa, the Papal States, Spain and eventually Venice smashed a powerful Ottoman Turkish invasion fleet at the mouth of the Adriatic. Pope Pius had called on Catholics to pray the rosary for victory, and each year in October the Feast of Our Lady of the Rosary recalls these events.

The Battle of Vienna took place on Sept. 12, 1683, after a two-month siege by the army of the Ottoman Empire. Pope Innocent XI had labored to assemble another Holy League. Playing a central role in the fighting were Polish cavalry led by King John Sobieski, whose gallant charge broke the back of the Turkish attackers.

“The motivation was high,” a commentator writes, “as this war was not as usual for the interests of kings, but for Christian faith.” That is in marked contrast with the comparative indifference of today’s secularized West to the genocidal assault on Christians in places like Syria and Iraq.

Yes, jihadists are only a small part of the world’s 1.6 billion Muslims. But as events like 9/11 and the terror attacks in Paris, San Bernardino and a growing number of other places — now including Brussels — make all too clear, these fanatics are determined and deadly. They embody a version of Islam that, as one writer remarks, “really does want to conquer the world.”

Are we then witnessing the opening stage of the much-heralded clash of civilizations? If so, that suggests a surprising conclusion: the clash of civilizations, in the end, may turn out to be a clash of secularism and fundamentalism. History is unpredictable and often very strange.

Russell Shaw, a contributing editor to Our Sunday Visitor, writes from Washington, D.C.