> “Theft, blood feud, it makes no matter why. It is an ancient wound.” —Sherif Ali to LT Lawrence (Lawrence of Arabia)

Although said in a different context, Sherif Ali’s words accurately capture the basic motivations behind the recent unpleasantness between Iran and Saudi Arabia. The enmity between the two branches of the Muslim religion championed by these two nations — Arab, Sunni Saudi Arabia on one side and Persian, Shiite Iran on the other — is one of the oldest wounds in the world. The Sunni-Shiite divide predates by many centuries the existing political boundaries in the Middle East, and helps explain why Iran and Saudi Arabia would fight over a pile of rocks and sand like Yemen, take sides in the Syrian civil war, or nearly come to blows over the execution of a mid-level Shiite cleric in Saudi Arabia.

As a result of this ancient wound, the Persian Gulf and the broader Middle East have been locked in a kind of Sunni-Shiite Cold War for centuries, with occasional crises and flares leading all the way to open war. Yemen, Lebanon, Iraq, Bahrain and Syria are just the latest battlefields where Iran and Saudi Arabia (along with her Sunni allies) have worked against each other, some (Lebanon) mostly through proxies like Hezbollah and others (Syria) with a de facto military deployment of thousands of Quds Force fighters led by General Qassem Soleimani. In 2011, Saudi Arabia deployed ground forces and Kuwait deployed naval forces to assist Bahrain in putting down a Shiite uprising, and the UAE assisted Saudi Arabia recently in Yemen.

Added to the ancient wound is the modern political shape of the Persian Gulf, where there are only two kinds of governments: Sunni monarchies and Iran’s Shiite theocracy (it remains to be seen where Iraq will fall). Sunni Arab monarchies all view the Shiite theocracy in Tehran as a mortal threat, which was one of the principal reasons Saddam Hussein invaded the newly formed Islamic Republic in 1980 with the moral if not military support of Sunni monarchies. They all fear their own substantial Shiite minorities will follow Iran’s example and rise up in revolution, a threat nearly realized in Bahrain in 1981. An additional huge bucket of gasoline tossed on the fire is Iran’s looming arrival as a nuclear power — thanks to Barack Obama — which all of Iran’s neighbors view with alarm.

Which leads to the latest flare-up over Saudi Arabia’s execution of the Shiite cleric Nimr al-Nimr last weekend. Al-Nimr was known for virulent anti-Saudi rants and had openly called for Shiites to rise up against the Saudi kingdom. Following his execution, a mob in Tehran attacked and ransacked the Saudi embassy as Iranian security forces stood aside and did nothing. This is standard political theater in Iran — an outraged mob moves to attack an offending nation’s embassy (American in 1979, British in November 2011, Danish in February 2006, etc.) and the security forces watch and wait until finally moving in and making some pro forma arrests.

Both sides cast blame and aspersions on the other (Supreme Leader Ali Khamenei’s warning of “Divine Revenge” receives top points for style) and then kicked each other’s diplomats out of the country. Sudan and Bahrain joined Saudi Arabia in expelling Iranian diplomats, and Kuwait recalled its ambassador from Tehran.

How much farther this latest flare-up will go remains to be seen, but it’s all part of the ongoing struggle between the Saudi-led Sunni bloc and Iran.

By 2010, Iran had finally recovered from the devastating effects of the Iran-Iraq War, rebuilt its military, cemented its control over Lebanon, seen hated enemy Saddam Hussein hanged, and most importantly survived the Bush administration’s time in office without harm. Since 2010, Iran has successfully played Barack Obama and the UN like a benju, not only avoiding harm but getting formal approval for its nuclear program starting in just 10 years as well as more than $100 billion in sanctions relief. It has improved relations with Russia and China, taken control of Iraq’s nascent government, and expanded its influence into Yemen and Syria. At the same time the United States has let our strategic alliance with Saudi Arabia wither so that Obama could achieve his nuclear deal with Iran. Indeed, after the embassy attack, the first formal reaction from Secretary of State John Kerry was to criticize Saudi Arabia!

Overnight, Iran has claimed Saudi planes bombed its embassy building in Yemen. It’s not clear if there are the usual diplomatic staff in the building, though it is supposedly occupied by Iranian-backed rebels.

We are hopeful that this latest flare-up will end with nothing more serious than insults and out-of-work diplomats. But it is a useful reminder that behind every action between Iran and her Sunni neighbors there is the potential for unequal over-reaction, and that as bad as the Middle East may seem on any given day, it can always get worse.