Behind the Islamic State’s murderous campaign of jihadi chaos, past the shattered European Union, veiled by America’s police shootings, protests, and mass shootings, lurks the skulking husk of the Syrian government, still barrel bombing, gaining ground, suddenly, quietly, reconquering Syria.

What a difference a year makes. Once Assad was clearly on the ropes: his depleted army unable to put out all the rebellious fires within his domain, his Russian and Iranian allies seemingly unable to save him, the Islamic State’s butchers sharpening their cleaves upon the antiques of Palmyra while his more moderate rebel foes began an offensive towards his Alawite stronghold of Latakia.

Then came the Russians, who made a point of decisively changing the war’s dynamic. Shoring up the wavering Syrian army battlelines and deploying massive air power, Vladimir Putin carpet bombed Assad’s enemies while his officers and soldiers stiffened the Syrian army’s spine. Given such support, the Syrian army began the slow crawl back from oblivion, recapturing key Palmyra from the Islamic State, blunting the rebel offensive into Latakia, and even, recently, entering Raqqa province, where the capital of the Islamic State lay.

Now Assad is closer than ever to recapturing the greatest prize of all. Once the largest city in Syria, now, like the country itself, a husk of traumatized survivors and ruined world heritage sites, Aleppo has been under siege since July 2012 – four brutal years now of back and forth sniping across the same bullet-pocked streets, both sides desperately trying to complete an encirclement around the other. Now Assad looks to have cut off the rebels, and if his forces hold, he will be master of Aleppo once more.

So now the question is, how will the world respond? But let’s get specific first and note “the world” is a journalistic cliche that means nothing.

Whenever journalists use that term, they often mean the United States and its alliance networks, the United Nations, or, more often, nothing at all – as if the Central African Republic or Bolivia have much of a stake in the outcome of the Syrian civil war. This unitary language belies the reality: different places need different things from Syria.

We should thus start with the country that is most capable: the United States.

And the ugly geopolitical reality is that the United States can let Aleppo fall to Assad.

The U.S. cannot tolerate the Islamic State, whose open goal is attacking America and its allies. Left alone, IS would try to overthrow Turkey, a key NATO ally, as well as U.S.-aligned Gulf states. Were IS a localized force, obsessed with killing Shi’a alone, the U.S. would moralize, but be less geopolitically interested: local wars can stay local as far as the U.S. under Obama is concerned.

This is a key reason why the United States hasn’t made much of an effort against Assad: Assad’s war is local – hyperventilated on social media as some kind of Good vs. Evil contest for the soul of the Arab world, but in reality just another dictator putting down yet another uprising against his inevitably incompetent rule. Assad will not take Aleppo and turn his forces upon the U.S. or its allies beyond Syria itself.

Were Aleppo about to fall to the Islamic State, the United States would be rallying as it did to save Kobane in northern Syria in 2013-14. There, the U.S. launched a large air campaign to preserve the city’s Kurdish fighters – because IS would have used Kobane as a base to attack Turkey or beyond. Yet Assad’s very local goals precludes a massive American retaliation for his siege on Aleppo.

But there is another conundrum for Syrian rebels hoping beyond hope that this siege will finally rally the West to their side: the unsavory nature of Syrian rebels themselves. In northern Syria, the Free Syrian Army is more or less nonexistent – it’s a motley collection of militias who have under them their fair share of war crimes. Barrel bombs they do not have, but the record has shown that when given the opportunity, these groups murder Assad supporters just as readily as Assad bombs their families.

For the United States, the bad propaganda of aligning with such forces outweighs the strategic gains of halting Assad – because even if Assad does subdue Syria again, it merely returns the situation to the status quo ante, which is hardly intolerable to the U.S. A ruined Syria under Assad will take a decade or more to return to its pre-war strength, which even in 2010 was grossly outmatched by Turkey, Israel, and the United States.

On the other hand, to get caught supporting rebels who might turn into future Islamic State commanders could undermine the budding relationship between D.C. and Tehran, and will certainly hinder America’s attempts to prod its NATO allies to support its strategic goals in the Middle East.

That much of northern Syria is actually under al-Nusra Front control – an al-Qaeda affiliate – compounds the equation. The only “good” guys in the north as far as the U.S. is concerned are the Syrian Democratic Forces, a collection of Kurdish, Arab, and other minority forces that are mostly gearing towards fighting the Islamic State. While an SDF affiliate, the Kurdish YPG, does hold ground in Aleppo, they do so under a cease-fire, protecting Kurdish residents but not taking part in the active fighting – they are, so far, not subject to Assad’s counteroffensive.

Moreover, America is quite distracted right now: a divisive election year and low race relations have sapped the electorate’s ability to focus on foreign affairs. Even the Orlando shooting, with its Islamists overtones, has receded in the public mind. Obama is deploying what little geopolitical capital he has left in his term to retake Mosul, sending more troops to Iraq in what may eventually reach some 4,600 soldiers. To recapture Mosul before the election is both good politics and good use of what remains of Obama’s lame duck presidency, taking priority over any pushes to save Aleppo.

Meanwhile, in the U.S.-aligned Sunni world, the war is not just a local affair.

There Sunni forces that originally supplied the now-mostly-defunct FSA are divided between the Saudi-led Gulf Arab bloc and Turkey. Both agreed that Assad had to go; both had regional ambitions that propelled them into Syria. But of the two, it was Saudi Arabia that viewed Syria’s civil war as both a greater opportunity and a greater threat.

This is because Turkey could always take or leave Syria as a sphere of influence: to gain a pro-Turkish government in Damascus would have been quite the boon, bolstering Turkey’s strongman president Recep Erdogan while putting the brakes on Kurdish ambitions to carve out yet another Kurdish statelet on the Turkish border (the other being northern Iraq, a nearly-there Kurdish state). Much like the United States, Erdogan believed history was on the side of the rebellion; the track record of Arab ‘republic’ dictators in 2012, when the civil war began in earnest, was 0-4 (Tunisia, Egypt, Libya, Yemen).

But that didn’t pan out; instead, geopolitical space emerged in the chaos for Syrian Kurds to suddenly emerge as a powerful faction. These forces were loosely aligned with Kurdish rebels in Turkey itself. Domestic Turkish politics propelled Erdogan to whip up anti-Kurdish sentiment at home, essentially killing a peace deal with Turkish Kurds, so his party could win the November 2015 elections.

Like the United States, and for similar reasons, Turkey can live with a status quo ante. With Kurdish separatism returning to battle, it’s becoming increasingly clear that’s the best Turkey can hope for. It is not desirable that Russia, Turkey’s Black Sea rival, has expanded its power base in Syria, but that concerns America too, and so Turkey knows it doesn’t have to face down Moscow alone.

This is a key reason why Turkey won’t panic as Aleppo crumbles. Turkey may loosen the border and supply the rebels of its choice, but it will hardly call for an invasion or a no fly zone.

Saudi Arabia, on the other hand, does not see Syria as a war it can afford to lose.

For both America and Turkey, to fail in Syria is to change little for either of them: thwarted ambitions and hurt pride at most. But for Saudi Arabia, a unified Syria under Assad constitutes a major defeat.

That’s because Saudi Arabia sees Syria as part of a live-or-die proxy war against Iran. Saudi Arabia’s young Crown Prince Mohammed bin Salman, the de facto leader of Saudi Arabia (his father, King Salman, seems like he’s lost his mind), believes, probably correctly, that Saudi Arabia is rapidly reaching an inflection point of no return. He must reform Saudi Arabia internally to prevent the collapse of the monarchy; meanwhile, he must push back and assert Saudi power externally to prevent regional foes from taking advantage of Saudi’s reorganization and accompanying weaknesses.

Iran, as an Islamic Republic, would benefit immensely from the collapse of the House of Saud; it would leave no power left able to claim to stand for Islam. (That Iran is Shi’a is irrelevant in this regard; ambitious Iranian elites know they don’t need to convert Sunnis to Shiism to get the prestige of being Last Man Standing in the Islamist world). This means that Iran looks to knock down Saudi power wherever it can. Moreover, Iran knows that Saudi Arabia is the cradle of much of Sunni supremacism; to destroy the House of Saud could dry up the ideological well from which arch-Shi’a foes like the Islamic State sprung.

To lose Syria back to Assad would openly display Saudi weakness in a way no one could ignore. Anti-Saudi forces in Iraq, Yemen, and Bahrain would take heart; Iraq would readily and permanently slide into Iranian orbit, while Yemen’s always shifting tribes might decide their lot would be better under the Persian aegis. Most worryingly of all, the Shi’a of Bahrain, as well as Saudi Arabia’s Eastern Province, would have a stark example of the low quality of Saudi power. They would push back, and hard, causing fissures in Saudi Arabia that the Kingdom can ill-afford as it tries to save its despondent economy.

This is to say nothing of Saudi influence in the Arab and Muslim world. Should Saudi Arabia fail, regional allies in the Gulf Cooperation Council, like Kuwait, Qatar, and the UAE, will have much greater incentive to tie their geopolitical futures to the United States rather than to any of Saudi’s pan-Arab political projects. Distant powers like Sudan and Pakistan, long reliant upon Saudi largesse to balance budgets, will view Riyadh as a sucker at best, to be exploited at will, and a basket case at worse, a crazy old rich man to be taken advantage of before he completely self-destructs.

Meanwhile, Islamist foes of Saudi Arabia will see a brittle kingdom ready to be taken down: they will organize to strike. The suicide bombings of Eid were mostly unsuccessful, but they prove an Islamic State operational capability to hit Saudi targets.

This will force the Saudi hand; to lose Aleppo is to open the door to defeat. It is reasonable to assume the Saudis will deploy whatever force they can to ensure that does not happen.

Thus we can expect America and Turkey to mostly sit by while Saudi Arabia does the heavy lifting of saving Aleppo.

This may be beyond Saudi Arabia’s capacity: already bogged down in Yemen, not terribly competent in statecraft, Saudi elites risk overplaying what little hand they have left. That does not mean they know as much; Saudi government policy has rarely been terribly reflective. That increases the chances of it happening. As the siege of Aleppo turns in Assad’s favor, the Kingdom, and not NATO, will be where rebel salvation may lie. Whether Saudi Arabia can save them will remain to be seen.