Terrified at the prospect of an economically resurgent, potentially nuclear-armed Iran and a looming Shia-led uprising in its own oil-rich Eastern Province, Sunni powerhouse Saudi Arabia this week executed its leading Shia cleric, Sheik Nimr al-Nimr.
It was a dramatic, last-ditch effort to alter the balance of power in the Middle East, away from Iran and in favour of itself and its fellow despotic Sunni Gulf regimes.
Al-Nimr, after all, was the most prominent, popular and revolutionary of the kingdom's Shia leaders, and had close ties to the mullahs in Iran - where he was educated and had lived in exile during the 1990s.
Moreover, although he had recently renounced violence and was clearly executed on trumped-up charges of leading an armed uprising during the so-called Arab Spring, he had for decades openly called for the Eastern Province to secede from the Saudi state and for the overthrow of the House of Saud.
Crucially, during the 1980s and 1990s, al-Nimr was a leader of Hizbollah al-Hejaz, a terror group funded by Iran that aimed to bring about an Iranian-style theocracy not just in Saudi Arabia but also in Shia-majority Bahrain and in neighbouring Kuwait, where roughly one third of the population is Shia.
Hizbollah al-Hejaz, moreover, was implicated in the early 1980s in an aborted coup in Bahrain, a failed attempt to assassinate the emir of Kuwait, and numerous terrorist attacks inside Saudi Arabia itself.
The Western media may have forgotten this dark period of history in the Gulf, but the local regimes certainly have not.
What sealed al-Nimr's fate was an extraordinary speech he gave in 2012 following the death of interior minister Prince Naif. Al-Nimr said the event should be celebrated, adding that the prince would rot in hell for eternity.
He was, then, the perfect candidate for the Saudi regime to make an example of, with two key strategic goals in mind.
The first was to evoke the fear of Iranian meddling to instigate a full-blown sectarian showdown. Bahrain, Kuwait and the United Arab Emirates have already cut ties with Tehran.
The other was to send an unambiguous message to the Shia of the Eastern Province: all dissent from them will be crushed without mercy.
The initial reaction among the Shia minority to al-Nimr's execution has been remarkably muted, with just a few hundred locals marching in his home town and brief clashes with security forces.
That should not come as a surprise.
For while the Eastern Province is the House of Saud's Achilles heel, the Shia there are equally mindful that the only thing between them and the genocidal lunacy of Daesh is the Saudi royal family that oppresses, but does not massacre, them.
At the same time, there remains the risk that the Saudi royals miscalculated in executing al-Nimr.
For this new sectarian standoff could yet mushroom into a direct conflict between Saudi Arabia and Iran, as the proxy wars they are fighting in Syria and Yemen spiral out of control and the prospects for peace deals and common ground are crushed.