@Selsky it is a very complicated conflict these days. Was not able to find a single good summary, but these guys have been covering it in depth for a few years. This article does give a brief rundown on the first few years but doesn't give much detail on Turkey and Russia's involvement: https://warisboring.com/obamas-legacy-in-syria-a-shattered-country-and-a-looming-victory-for-assad/