The Syrian conflict, though deliberately obfuscated, was probably primarily a conflict between Russia-backed Iran and US-backed Saudi Arabia. Wahabism is an arm of the latter.
Of course, this would have isolated and aggrovated Russia further, and Assad knew that. Nevermind that Syria is within range of Russia's missiles. He also knew what became of Sadam Housein (once an ally to the US) once he was of no use to the West.
In any case, causing a civil war inside a country just to punish a leader for making calculated, reasonable choice is criminal and evil.