In the early hours of Thursday morning, Saudi Arabia bombed positions in Yemen held by Houthi militias, a rebel force that had already thrown out sitting President Abed Rabbo Mansour Hadi from the capital, Sanaa, and was on the verge of ousting him from his last redoubt in the key southern port city of Aden.
"We will do whatever it takes in order to protect the legitimate government of Yemen from falling," said Adel al-Jubeir, Saudi ambassador to the United States, at a media briefing on Wednesday night.
Saudi media reported that the campaign, dubbed Operation Decisive Storm, was coordinated with a coalition of other Arab countries — primarily Sunni Gulf states already closely allied with Riyadh.
The airstrikes, involving more than 100 Saudi jets, targeted air fields and bases near Sanaa and Aden and reportedly disabled the Houthis' air force. It's unclear to what extent there may have been civilian casualties, given the urban density of the areas that were hit.
The Saudi campaign has been characterized by some as the latest escalation in a proxy war with Iran, the Middle East's Shiite power, which has backed the Houthis. It also takes place at a moment when Iranian proxies in Iraq are receiving American support in their fight against the jihadists of the Islamic State.
All the while, the worrying disintegration of the Yemen, one of the Arab world's most impoverished countries, continues.
The battle for Yemen
The Saudi airstrikes may weaken the Houthis' capabilities and stem their advance in southern Yemen, but they can't defeat the movement.
The Saudis say the bombardment is likely just the beginning of their offensive. If they hope to force the Houthis' surrender, then a substantial ground incursion would be needed.
The Houthis' slow-motion rebellion picked up steam after mass protests and military defections led to them seizing Sanaa last September and later dissolving parliament.
The Houthis represent a political movement closely associated with the Zaidi sect, a Shiite offshoot whose imams traditionally held sway in northern Yemen for centuries. But their rebellion has always been motivated more by an interest in turf, money and power than ideological preeminence.
Frustration with the government of Yemen's long-ruling former president, Ali Abdullah Saleh, saw a sustained insurgency take root over the past decade and half and gained strength following Saleh's resignation after a pro-democracy uprising in 2011.
But the Houthis felt marginalized by the new status quo, which was ushered in by the Saudi-led Gulf Cooperation Council — a grouping of Sunni Gulf states — and put Hadi in power.
Under Hadi's fragile "national unity" government, Yemen was anything but united.
Al-Qaeda-allied militias and Sunni tribes waged their own insurgencies in Yemen's south, while the Houthis built their power. Their eventual takeover of Sanaa and large parts of Yemen was reinforced by alliances with other disaffected tribes and factions.
There are strong suspicions that Saleh and his supporters, for so many years at odds with the Houthis, have played a significant role in enabling their rise. Military units loyal to Saleh sided with the Houthis against Hadi's government.
In an interview with The Washington Post earlier this year, Saleh denied any direct alliance with the Houthis. But he pinned Yemen's woes on Hadi.
"It’s only natural that the Houthis are in control due to the absence of a strong state," Saleh said.
The Houthis "had the most guys with guns," wrote Yemen expert Gregory Johnsen last month. "All that was left was for them to consolidate their gains."
The Middle East's widening gyre
A complex, fractured conflict in Yemen has been overshadowed by wider regional tensions.
The coalition cobbled together by the Saudis looks very much like a Sunni bloc — here's a map circulated by Saudi-owned Al Arabiya News, indicating what various states are contributing to the fight.
Iran, Saudi Arabia's regional foe, swiftly warned Riyadh against continuing its offensive.
"Military action from outside of Yemen against its territorial integrity and its people will have no other result than more bloodshed and more deaths," said Iranian Foreign Minister Mohammad Javad Zarif.
A statement from the embattled Syrian regime of President Bashar al-Assad, a key Iranian ally, decried the Saudi royal family's "blatant aggression on Yemen."
Russia, Assad's main friend on the U.N. Security Council, urged a cessation in hostilities and called for "a broad national dialogue" in Yemen, though no such mediation looks anywhere in sight.
Perhaps the most revealing set of statements regarding Yemen came from Lebanon, a country that for years has been a microcosm of the Arab world's larger political and sectarian divisions.
Hezbollah, a powerful Shiite organization backed by Iran, said the Saudi "adventure" in Yemen lacked "wisdom and legal and legitimate justification."
"Iranian meddling in Yemen necessitates an Arab reaction," he added.
It's not totally clear to what extent the Iranians have fueled the Houthi uprising, which, as explained above, has considerable indigenous support.
Kenneth Pollack, a senior fellow at the Center for Middle East Policy, writes, "The Iranian role has been greatly exaggerated in what is first and foremost a Yemeni civil war."
Whatever the case, the Houthis are using the moment to pin their colors to the national mast.
"We will react against Saudi oppression in all ways we are capable," said one Houthi spokesman, quoted by the Wall Street Journal. "Yemeni blood is not cheap. Saudi has announced war in Yemen."
The awkward job of the United States
The Saudi-led campaign in Yemen comes at a particularly sensitive moment for the Obama administration.
U.S. officials are in the middle of critical meetings this weekend with Iranian counterparts in Switzerland, attempting to thrash out a long-sought deal over Tehran's controversial nuclear program.
Moreover, as Saudi bombs fell on Iranian-backed militias in Yemen, the U.S. conducted airstrikes in Iraq that directly aided Iranian-backed militias fighting the jihadists of the Islamic State.
The United States has so far offered logistical support and intelligence help to the Saudi-led effort and issued statements earlier condemning the Houthi advance on Yemen's "legitimate government." Over the past few years, the United States has seen its conflicting commitments to Middle East democracy, regime change, security and political stability get entangled in a mess of regional crises. The irony of the present was best illustrated in a tweet by Lebanese satirist Karl Sharro.
That diagram may not be totally accurate, but the headache it'll give you when sorting it out is probably shared by strategists in Washington.