One point of view - inaccurate as usual as the Bashar al-Assad government is NOT universally recognized as the legitimate representative of all the Syrian people.
The Syrian National Council (SNC), a Syrian opposition coalition based in Istanbul, Turkey, formed in August 2011 during the Syrian civil uprising (which escalated into civil war) against the government of Bashar al-Assad, is recognized by 27 UN members, the Republic of Kosovo and the European Union as a legitimate representative of the Syrian people in the midst of the Syrian Civil War, with three of those being permanent members of the Security Council (
https://syriancouncil.org/; https://en.wikipedia.org/wiki/Intern...tional_Council).
The Syrian Democratic Forces is the self-bestowed name for the official defense force of the Autonomous Administration of North and East Syria. It is an alliance of forces formed during the Syrian civil war composed primarily of Kurdish, Arab, and Assyrian/Syriac, as well as some smaller Armenian, Turkmen and Chechen forces. It is not a name given by the US to any group.
The fact that Russia illegally occupies and annexes Crimea, and recognizes parts of Luhansk and Donetsk regions as "People's Republics," doesn't make presence of Russian armed forces on Ukrainian territory legal.