An Alawite Syrian army officer warned Mr. Assad is on the cusp of ceding what was left of Syria’s sovereignty by welcoming a greater Russian role on top of an already robust Iranian one.

“Russia’s intervention won’t end the war,” he said. “It will divide the country.”

In such a scenario, the Alawites along with other minorities would be relegated to a western corridor connecting Damascus to the coast, as most Sunnis are pushed out to the rest of the country, where Islamic State and others will fight each other for control.

The rallying of Iranians and Russians to Syria’s depleted and hollowed out army represents a pivotal phase in the conflict.

Khattar Abou Diab, a professor of political science at the University of Paris, said Syrian troops and their foreign militia allies are unlikely ever to regain control of the whole country, turning Russia’s gambit into a dangerous test of wills with the West.

“If they destroy the moderate opposition, then they put everyone in front of two choices: Assad or ISIS,” he said, referring to Islamic State. “If this fails then plan ‘B’: Rule part of Syria and carve out the Alawite state.”