Historians employ a striking term — the "Great Game" — to describe the fierce 19th century test of wills that took place in Afghanistan and across central Asia between tsarist Russia and then-colonial power Britain.
With its overtones of guile and pitiless cynicism, the phrase is a relic of the past — but in some ways, it distills the harsh political realities surrounding the military and diplomatic jousting over Syria.
Against a backdrop of ruined cities and biblical floods of refugees, the competing and overlapping interests of an array of outside actors have played out over nearly six years of grinding conflict in Syria. Alliances have shifted; rivalries have sharpened and eased; even highly predictable events contrive to surprise.
The smoking rubble of east Aleppo, and the suffering of hundreds of thousands of civilians caught in war's path, in no way resemble a game. But the fall of the northern city to Syrian government forces and their allies has opened a new chapter in a power struggle that extends far beyond the country's borders.
Here is a look at some of the countries that see themselves as having a stake in Syria's war, how their actions have shaped the fighting to date, and how they might seek to influence the conflict going forward.
President Vladimir Putin's year-old decision to intervene militarily in Syria tipped a largely deadlocked battle sharply in favor of Syrian President Bashar Assad. Devastating Russian-led bombardment was a key factor in the fall of Aleppo, once Syria's largest city and its commercial capital before the war.
Analysts see Putin's actions as part of a broader effort to expand Russian influence across the Middle East, paralleling aggressive moves elsewhere, including in Ukraine.
Russia's Mideast muscle-flexing carries risks of getting bogged down militarily in regional quagmires. But becoming a prime power broker in Syria fits in well with Putin's strong desire to reassert great-power status, especially when his regional ambitions have encountered virtually no pushback from President-elect Donald Trump.
When it comes to Syria, the imminent Trump presidency represents a major unknown. His pre- and post-election comments on Syria have been confusing and sometimes contradictory. But the positions he has articulated appear to point to acceptance of Assad's continued rule, the possible withdrawal of support from previously U.S.-aided rebel factions and a willingness — even eagerness — to partner with Russia in fighting the Sunni Muslim militants of Islamic State.
All those steps would be reversals of the Obama administration's stance. Many critics consider Syria a major stain on the outgoing president's legacy, as years of U.S. efforts to halt the bloodletting have been ineffectual.
Underscoring a dearth of American influence in the Syria arena, Secretary of State John F. Kerry waged a fruitless battle to halt the indiscriminate bombardment of Aleppo, which he and some U.N. diplomats have called tantamount to a war crime. But the bombing didn't stop until the last rebel-held parts of the city were about to fall.
NATO ally Turkey has joined in the U.S.-led coalition confronting Islamic State. But President Recep Tayyip Erdogan has made no secret of his anger at the West over issues including refugees and ongoing human-rights criticisms as he carries out a massive purge of political opponents in the wake of a coup attempt against him in July.
Turkey shares the Obama administration's desire to see Assad's rule end. But that wish is overshadowed by a separate, overriding concern on Ankara's part: preventing the establishment of a de facto Kurdish statelet on the Syrian side of Turkey's border, something Erdogan fears would embolden his country's own sizable ethnic Kurdish minority.
Turkey has drawn closer to Russia in recent months, and even the assassination this week of Russia's ambassador to Turkey by a gunman voicing anger over Aleppo did not appear to harm that rapprochement. The day after the murder of envoy Andrei Karlov in the Turkish capital, Turkey joined Russia and Iran in issuing the "Moscow Declaration" — a bid to broker and guarantee a Syrian peace accord.
Assad's minority Alawite sect is an offshoot of Shiite Islam, and Iran, the regional Shiite center of gravity, supports armed groups including Hezbollah, whose battle-hardened forces have fought alongside Syrian government troops since the war's earliest days. Iranian-trained Shiite militias also played a substantial part in the battle for Aleppo, and the United Nations has accused some of them of taking part in atrocities.
Iran has signaled its intent to join with Russia and Turkey in setting the terms of any Syrian peace accord, but Iran has its own worries about Trump. He has threatened to scrap the landmark nuclear accord between Iran and Western powers, which led to the easing of crippling sanctions.
Despite Trump's declared willingness to partner with more or less anyone in fighting Islamic State — which considers Shiites heretics — the president-elect could prove hostile to the notion of Tehran as a main player in any winding down of the Syrian war.
Saudi Arabia, together with Persian Gulf allies such as Qatar, has backed armed groups trying to topple Assad. But the kingdom has been preoccupied for nearly two years with a messy war in Yemen, leading a Sunni Arab coalition that has sought to crush Shiite-aligned Houthi rebels who seized control of much of the poor but strategic country at the tip of the Arabian Peninsula.
Saudi Arabia, an important U.S. ally in the region, has signaled alarm over the prospect of a Russian- and Iranian-brokered Syria accord. Earlier this year, a former senior Saudi intelligence official, Prince Turki bin Faisal al-Saud, told a forum at the Middle East Institute in Washington that any Trump deal-making in concert with Russia and Iran over Syria would be "the most disastrous step possible." He urged Washington to turn instead to its long-standing allies in the region.
Members of the European Union participate in the U.S.-led coalition fighting Islamic State. But despite being been roiled by hundreds of thousands of refugees and asylum-seekers, with Syrians making up the largest share of the arrivals, the bloc has wielded little real influence in efforts to end the fighting.
Neighboring Lebanon and Jordan have absorbed huge numbers of Syrians fleeing the conflict; in tiny Lebanon, Syrians now make up about one-fifth of the population. The destabilizing effect of the war and the wave of refugees have raised worries in Jordan, where U.S. ally King Abdullah faces a rise in radical Islamist movements.
Israel has for the most part practiced a studied neutrality in the Syria conflict. Its formidable army keeps a watchful eye on the Syrian side of the Golan Heights, Israel's doorstep, where some Syrian rebel factions in residence have ties to Al Qaeda. Prime Minister Benjamin Netanyahu has acknowledged that Israel has struck Hezbollah targets inside Syria with the aim of preventing the group from obtaining advanced weapons. Israel has also provided medical care to Syria's war-wounded, rebels and civilians alike.