Saudi Arabia dominates the culture of mainstream, majority, Sunni Islam - and has been an American military ally since WWII. Iran dominates the world of Shiite Islam and has been openly hostile to the West, and to pro-Western Arab nations, for almost 40 years. The open hostility between the two regional rivals takes many forms, including a proxy war in Yemen, just to Saudi Arabia's south, and in Iraq, and in Syria, and several other battlegrounds. If this progresses to war, leadership of the Islamic world is ripe for the taking, and this could escalate to Nostradamus' prophetic fulfillment of WWIII.
Over the weekend, the Saudi King purged the government of dozens of high ranking princes and officials: "In a shocking development, late on Saturday the Saudi press reported that prominent billionaire, member of the royal Saudi family, and one of the biggest shareholders of Citi, News Corp. and Twitter - not to mention frequent CNBC guest - Al-Waleed bin Talal, along with ten senior princes, and some 38 ministers, has been arrested for corruption and money laundering charges on orders from the new anti-corruption committee headed by Crown Prince Mohammed bin Salman, while Royal princes’ private planes have been grounded. Among those fired and/or arrested are the head of National Royal Guards, Miteb Bin Abdullah, the Minister of Economy and Planning, Adel Fakeih, and Admiral Abdullah bin Sultan bin Mohammed Al-Sultan, the Commander of the Saudi Naval Forces."
As just reported at Zerohedge.com here: "This weekend's chaos in the middle east just got considerably more serious. Yesterday we detailed reports that the Saudis intercepted a ballistic missile over the nation's capital Riyadh... At the time, Al Jazeera reported that Yemen's Houthi rebels claimed responsibility for the attack, saying they launched the Yemeni-made, long-range ballistic missile Burqan 2-H (with a range of 500 kilometers) from the Saudi-Yemeni border before being intercepted. But tonight, according to a statement from the Saudi coailition carried by the state-run Saudi Press Agency, the missile that targeted Riyadh has been called "a direct military aggresion" by Iran against Sauid Arabia, that "could rise to be considered an act of war."
And America could be pushing the war: "The timing is fascinating. What better way to get the price of oil up before an Aramco IPO - which President Trump just happened to mention out of the blue. And amid increasing evidence of Saudi rapprochement with Russia and China - and the growing de-dollarization of the anti-unipolar world - a Saudi war with Iran would require the latter to be supported by Washington to survive... which perhaps could be quid pro quo for ending any chatter about the death of the petrodollar."
UPDATE: A few days later an article in the New York Times warned that tensions between the Saudis and the Iranians were raising “the threat of a direct military clash between the two regional heavyweights.” Jake Novak of CNBC said that a “direct conflict between Saudi Arabia and Iran, as opposed to the proxy war they’re fighting in Yemen, looks inevitable.”
I don't personally think a Saudi-Iranian war is imminent - but the press is certainly pushing the idea.