TEHRAN, IRAN - JANUARY 4: Demonstrators hold posters of Nimr Baqir al-Nimr during a protest rally against the execution of prominent Saudi Shia cleric Nimr Baqir al-Nimr by Saudi authorities, in Tehran, Iran on January 4, 2016. (Photo by Fatemeh Bahrami/Anadolu Agency/Getty Images)

The escalation of tensions between Saudi Arabia and Iran over the Saudi execution of a Shiite imam is only the latest episode in a 35-year old, low-intensity conflict between the two regional powers.

It is essentially a geopolitical struggle: Saudi Arabia and Iran are vying to dominate the Middle East's empire of oil and stake a place as a player among world powers. Saudi Arabia lonf held that position, but Iran threatens its status.

The competition took off in 1979, when the Shiite Islamic revolution triumphed in Iran. The mullahs in Tehran began to slowly spread their influence. They set themselves up as a rivals to the US, established Iran as a staunch enemy of Israel and supported Lebanon's Hezbollah militia, putting their influence -- and military muscle -- at the heart of the traditionally Sunni Middle East.

Sunni Saudi Arabia reacted by intensifying the spread of its own ultra-conservative Islamic ideology, Wahhabism, throughout the region. Riyadh supported friendly governments, funded mosques, trained preachers and backed Islamic insurgent and terrorist groups in places as far afield as Palestine and the North Caucasus.

In both countries, rule is maintained by strict enforcement of ultra-conservative Islamic social norms. Iranian clerics directly oversee politics and brook no dissent outside their ultra-puritanical version of Shiite Islam. The Saudi monarchy declares itself carriers of a true, purist Islam. Politics are confined to intra-family intrigue; while the Western press focused on the execution of the Shiite preacher Nimr al-Nimr, it should be noted that the 46 other victims were Sunni opponents of rule by the Saudi royal family.

The Saudi-Iranian competition evolved as a largely-ignored subtext to the intermittent interventions by the U.S. in the Middle East and the region's chronic instability. Following the disastrous American adventure in Iraq and the subsequent decline in US dominance, the Saudi Arabia vs. Iran conflict is taking center stage.

From the Saudi point of view, its influence is on a long losing streak, with most benefits accruing to Iran:

• Iran dominates Syria and backs its beleaguered president Bashar al-Assad with arms, commanders and client militias against Sunni insurgents. Saudi Arabia backs the rebellion but has been unable to insure its success.

• After the United States overthrew Saddam Hussein, he was replaced by a Shiite government with heavy Iranian influence. Saddam, while not a favorite of the Saudis, was at least seen as a buffer against Iranian expansion. A long-running Sunni insurgency has yet to supplant the exclusionist Shiite government in Baghdad.

• In Lebanon, Iran is the main military supporter of Hezbollah, the political party and militia that became the chief competitor to traditional Sunni power in the country. Christians in Lebanon are on the sidelines of this power struggle. After former Prime Minister Rafik Hariri threw off Lebanese dependence on Syria as a broker in Lebanese politics and turned instead to Saudi Arabia, Syria engineered his 2005 assassination. In 2008, when a subsequent Lebanese government tried to force Hezbollah to give up its private communications network and end its use of Beirut airport as a conduit for arms, Hezbollah sent its allies to occupy West Beirut, symbol of Sunni economic and political power.

• Saudi Arabia regards the Shiite rebellion in Yemen against a Saudi-backed government as a cat's paw for Iranian intervention. Riyadh struck back with its current, ineffective bombing campaign and support for pro-government mercenaries.

• Iran replaced Saudi Arabia as a chief sponsor of Hamas, the anti-Israel Palestinian faction that rules the Gaza Strip.

• Last but not least, the US-led deal to end Iran's nuclear weapons program opened the way for Iran to reenter the global oil market and strengthen its economy. The US put no brakes on Iran's aggressive foreign policy.

The religious aspect of the struggle is especially devastating to coexistence among Muslim civilians. The history of Sunni-Shiite rivalry dates from the earliest years of Islam. Wahhabi Saudi Arabia has been a main promoter of anti-Shiite dogma, declaring Shia followers to be heretics. This concept has helped fuel conflicts between Sunni and Shiite communities wherever they meet. It is reflected in the vicious religious cleansing taking place in both Iraq and Syria. Christians, largely bystanders in this conflict, are nonetheless victims as each side seeks to purify its area of control.

In the old days (i.e. from World War I to the end of the US occupation of Iraq), some foreign power might have been willing and able to step in and impose some sort of self-interested, colonial order on such a situation. Not now. The US is unwilling, Great Britain and Europe are effectively in retirement, and despite its recent flexing of muscle Russia is weak.

The best anyone can do it to try and keep the Saudi-Iran conflict from exploding into total war. But the proxy conflicts will continue.