Iran’s intervention in Syria has turned the Syrian civil war into a proxy conflict between the region’s Shia and Sunni. Iran’s intent is to transform Syria from an ally into a protectorate. Syria’s Sunni majority resented but tolerated an Alawite police state, but will fight to the death against prospective occupation by a foreign Shi’ite power. Saudi Arabia and Turkey will continue to pour resources and fighters into Syria to prevent an Iranian takeover. The Sunnis fear a regional Iranian reign of terror under a nuclear umbrella and will fight to the death to prevent it. The Shia-Sunni conflict in Syria may spill over into Iraq, where remnants of Saddam Hussein’s military leadership have armed and recruited a Sunni fighting force, and Lebanon, where a jihadist “Sunni Awakening” challenges Hezbollah.

Sunni-Shia conflict is not necessarily averse to American interests; as Daniel Pipes, the dean of conservative Middle East analysts, wrote April 11, “Evil forces pose less danger to us when they make war on each other. This (1) keeps them focused locally and it (2) prevents either one from emerging victorious (and thereby posing a yet-greater danger). Western powers should guide enemies to stalemate by helping whichever side is losing, so as to prolong their conflict.” (I made a similar argument last year.)

Everything changes, though, if Iran acquires nuclear weapons. Instead of a containable war of attrition, we will have an Iranian reign of terror under a nuclear umbrella. If Washington and other Western capitals are intimidated by Iranian terror capabilities (including the Iranian threat to disrupt Western oil supplies) without nuclear weapons, what can we expect from the feckless diplomats of the West if Iran has the option of nuclear terrorism?