Why do they hate … them? That is the question to ask in the wake of the slaughter of nearly 50 people by Islamic suicide bombers in a mosque in Quetta, Pakistan, on July 4.

This was no isolated local atrocity, no jihad against Zionist oppressors, no blow delivered by the underdog against American crusaders. These victims were poor, Pakistani and Shiite Muslims. Like the bombs set off in Saudi Arabia and Morocco a few weeks ago, this assault in southwestern Pakistan involved Muslims killing Muslims in the name of religion. It was part and parcel of an expanding civil war within Islam that is being fought across an extended region vital to U.S. interests.

Americans tend to think of their country as the center of global virtue. When Osama bin Laden’s henchmen killed more than 3,000 people on American soil on 9/11, politicians and pundits rushed to ask about Arabs in particular and Muslims in general: Why do they hate us?

But events since then have shown that this was too self-centered and exclusionary a reflex. Those who hate in this way hate much more than us. Their fury is part of a bigger picture that is succinctly and expertly treated by historian Bernard Lewis in his new book, “The Crisis in Islam.” As Lewis points out, the radicals have an entire world to destroy before their apocalyptic design of restoring the Islamic caliphate can be realized.

Instead of asking with embarrassing self-referential introspection why they hate us, American politicians and pundits should be pointing out that the first, most important line of this battle must be fought by Muslims in the battle for the soul of Islam.

The key to winning that battle lies in the mobilization of a revitalized Islamic mainstream that will reassert and protect itself from the extremists. Islam, as have other great religions, has periodically had to rescue itself from movements that would hijack an entire faith. This is such a moment.

The American way of life, U.S. support for Israel and Washington’s military power provoke specific animosities toward the United States by the jihadists. But their rage against those they consider fallen-away Muslims is as great. Apostates are the worst of all infidels.

Arab leaders who exercise power through the nation-states created in the colonial era are turncoats and usurpers. Islamic radicalism has become a vehicle for the power-mad, like bin Laden. Islamic moderation is the best antidote to their ideological poisons. The United States on its own cannot reform the Muslim world. Only Muslims can do that.

But Washington can be a catalyst to introduce change into the grim stalemate that now exists between the two main branches of Islam, the Sunni majority which control the governments and commerce of most Arab countries, and the Shiites who govern Iran but are downtrodden minorities elsewhere.

As long as the leaderships of both communities were absorbed in pan-Arabism, nationalist struggles and the Cold War, Islam was dormant as a political force. But in 1979, a Shiite theocracy took power in Iran after the overthrow of the shah and set off a chain reaction throughout the Middle East, the Persian Gulf and Central Asia by vowing to export its revolution.

The Wahhabist Sunni establishment of Saudi Arabia responded by pouring its oil wealth into a fierce counter-revolution. Muslim governments either sought to profit by taking funds from both contending factions or looked the other way and pretended no religious conflict was occurring.

The United States has largely stumbled its way into a central role in this conflict of religious extremes. Uncomfortable with admitting and analyzing the role of religion in politics abroad as well as at home, American policymakers rely almost exclusively on the region’s political authorities and U.S. military power as levers of policy.

Washington has been slow to capture the depth and breadth of the competing Islamic revolutions and their long historical roots. Lewis argues persuasively that the conditions that create movements like bin Laden’s al-Qaida are almost as old as Islam. They have more to do with the way in which the religion developed than with any particular “us.” We are stand-ins for and acolytes of the Muslims who are the main target of the radicals’ fury.

The entire political system that has prevailed in the Muslim world since the end of the colonial era is under attack. It is not up to Americans to decide if the survival of the nation-state, as it exists in Egypt, Pakistan and elsewhere, is compatible with Islam. That is a task for Muslims, who themselves should be asking, “Why do they hate us?”