Russia's military build-up in Syria is aimed mainly at propping up President Bashar Assad and helping him reinforce his threatened coastal heartland, where he is seeking to bolster the communities that form his power base as his army falters.
The Russian escalation has ended any prospect of Assad being ousted by military force, despite the near collapse of his army in the face of rebel advances, and will consolidate the de facto partitioning of Syria, most analysts believe.
Residents of the coastal city of Latakia, a stronghold of Assad's Alawite minority, say the increase in Russia's military presence began as early as June and, along with it, preparations for an eventual breakup of the country of 23 million people.
The population of Latakia has swollen fourfold during four years of civil war, and the government is now facilitating the settlement of other minorities such as Christians and Shi'ites.
But since most Syrians are Sunnis, those who flee to the coast are not allowed to move their civil registration there, a move designed to prevent the Sunni majority from becoming a threat to the Alawites, an offshoot of Shi'ite Islam.
With roughly two thirds of Syria controlled by mainly Islamist rebels, whether Syrian fighters backed by Qatar, Saudi Arabia and Turkey, or the cross-border Islamic State, it looks inconceivable that Russia could retake territory lost by government forces unless it were to commit ground troops.
That is not on the table so far, analysts say.
What does seem clear is that Russia's move was prompted by alarm that government forces were losing ground so fast that the survival of the Assad family, for decades Moscow's closest ally in the Middle East, was in question.
When Islamist rebels started to threaten Latakia, which is near the Russian naval base at Tartus, Moscow's only naval facility in the Mediterranean, the Kremlin decided to step in.
Russia's close ties to the Syrian government go back to the Soviet era when Moscow counted Bashar's father, Hafez Assad, as a firm ally. Even before the latest build-up, it had teams of military advisers and trainers on the ground.
Assad to Stay
Russia's plan is to help forces loyal to Assad hold and reinforce the Alawite enclave in the coastal and mountainous northwest, Syria-watchers say.
If Assad were pushed out of Damascus and the capital fell either to Islamic State or other Islamist rebels, Russia and the Syrian government's allies such as Iran and Hezbollah will have dug him a well-fortified fallback position in Latakia.
Amid uncertainty about President Vladimir Putin's goals in Syria, there are contrary opinions about whether Moscow intends to follow its show of regional force with a diplomatic initiative to end Syria's four-year civil war.
But there is a near consensus that Assad's forces were fading, and Russian intervention will accelerate the partition of the country into warring fragments.
The Russians were quick to send in air forces and more ground equipment, said Robert Ford, former U.S. ambassador to and then special envoy for Syria, who resigned because of differences with U.S. policy on Syria.
"It makes me think that the Assad regime was actually becoming very weak and the Russians became scared," he said.
While the Kremlin says its deployment is part of the international fight against Islamic State, its main goal is to boost Assad and defend Russia's beachhead on Syria's northwest coast, Ford said.
"Why would you put the air units in Latakia instead of Damascus if you want to fight the Islamic State?" he said. "Why do you send anti-aircraft equipment when the Islamic State doesn't have any air force?
"So it seems to me that this is designed to help Assad first," Ford said. After that they may attack Islamic State and other elements of the opposition in northwest Syria.
He saw no evidence that the Russians would jettison Assad and risk the stability of what remains of the Syrian state.
A former senior Syrian official said Assad had asked Russia to intervene "because he was desperate and the army was collapsing." Assad had briefed his loyalists that Moscow would provide reinforcements and weapons, and take command of the air force.
"The Russian intervention is to help Assad preserve the status quo, maintain the areas of the regime, the enclave," the former official said. He had doubts, however, about Assad's long-term prospects.
"This will allow the regime to continue with its policy of no negotiation with the opposition but it won't solve the problem."
Fawaz Gerges, Middle East expert at the London School of Economics, said the Russian action was a turning point in stiffening Assad's resolve that removed any prospect that he would leave the scene sooner rather than later.
"Contrary to what the United States, Turkey, Qatar and Saudi Arabia have been trying to say and do, the Russian intervention in Syria shows that Assad is not going anywhere," Gerges said.
At the same time, he said, the ramped-up Russian presence will reinforce Assad's feeling that neither the United States, Turkey, nor any other regional power will intervene enough to tilt the balance of power away from stalemate.
Yet Putin, who sees Syria as part of a wider Russian bid for influence in the Middle East, is taking a gamble.
"Russia now is taking big risks. Syria is a quagmire in which everyone is basically drowning. Everyone is losing and Syria could prove to be a graveyard for Russia's influence in the Middle East," Gerges said.
Many analysts believe that while Assad's external foes now realize he is going to stay, that does not mean they want to cooperate with Putin.
After Russia grabbed Crimea and divided Ukraine, some feel its surge back into the Middle East is a bargaining chip for its European agenda.
Ford said Washington would continue bombing Islamic State in central and eastern Syria, and working with the Syrian Kurdish militia. "I think the Americans are going to pretend that the Russians aren't there," he said.
"If I were Assad in Damascus now," said Gerges, "I know that I have my superpower ally with direct influence, direct presence in the heartland, in my birthplace."
Ayham Kamal, an analyst at Eurasia Group, agrees: "The Russian intervention will make it very difficult for anyone to push forward with regime change. Assad is there to stay, at the very least in a transitional capacity, and the rest depends on negotiations between the West and Russia."