To put it simply, The Syrian Civil War is a quagmire. There are alot of different factions at play here. It can be a little confusing to those getting into this topic to navigate. This guide hopefully will provide you with a brief overview of the situation down there as of today.
The Turks are against the Syrian Kurds and Assad and ISIS roughly in that order and nominally allied with the US however Russia has been recently trying to make friendly overtures towards them. The Turks mainly seek to quell the local Syrian Kurds to keep their own Kurdish separatist movement in check as well as gain a greater influence in the Middle East at the expense of Saudi Arabia, Qatar, and the other Gulf States as well as Iran. They sent a military intervention into Syria with the goal of fighting both ISIS and the Syrian Kurds. Recently, there has been an uptick in violence between the Syrian Kurds and Turkish forces as ISIS-held Raqqa nears collapse
Assad has, with the support of Russia and Iran, been focusing mostly on non ISIS rebels which are themselves a patchwork of different factions of shifting alliances running the gamut from hard core Islamists of a different ideological stripe from ISIS to secular militarists to straight up secular liberal democracy proponents. However the Syrian regime is also at war with ISIS but have largely let the US coalition fight them, keeping their military operations concentrated to the southern and western parts of Syria. Until the Russian intervention Syria government forces were on the brink. The Iranian militias supporting them “unofficially” were not enough to stem the tide. However the arms and military support from Russia allowed them to take the offensive and make considerable gains in the war. They are trying to stay out of the Syrian Kurds way as the Syrian Kurds have been the main force fighting ISIS with the perceived strategy of letting them fight it out and taking down the winner.
The Gulf States
The Gulf States (UAE, Qatar, Saudi Arabia, etc) generally back support and arm various rebel groups within Syria shifting their support as the map and battlefield changes. They tend however to support the hardcore Islamists as a way of staying “tough on seculars” They are also nominally allied with the US as ISIS and Iran are common enemies. They do this mostly to maintain their local hegemony over the region and to prevent Iran and non Gulf Muslim States (like Turkey and Iran) from gaining the upper hand, influence wise. Also as one of ISIS’s stated goals is the utter destruction of those states they must work with the US to prevent that.
Iran seeks to maintain its last foothold of influence in the Arab world (Iranians are Persians) and thus supports Assad as the Syrian regime was one of the few that had a pro Iranian policy. They are nominally allied with Russia as the two share similar goals of keeping the Syrian regime alive. They also are against ISIS as their special brand of Islam is not ISIS’s special brand of Islam so they fight their own completely separate battle against them. This is done mostly through unofficial militias as well as “Iranian volunteers.”
Russia also seeks to maintain its last foothold in the Middle East. Continuing it’s long-standing policy of warm water ports, it seeks to preserve the military base in Tartus that it has in Syria ( the Syrian regime has granted them military access and a base there) as well as gain new bases in Syria to continue its bid for control and access to the Eastern Mediterranean and the trade routes that pass through it. It also is against ISIS largely out of an outgrowth of the Chechen conflict (many former Chechen rebels went to ISIS after they lost.) As such they back the Syrian regime to the hilt against the Syrian rebels, ISIS, and the US and Gulf state interests roughly in that order and nominally work with Iran.
The Syrian Kurds are straight up fighting for their own country. Kurds are the largest and oldest “Stateless Nation”. They haven’t been able to form a state as traditional Kurdish lands straddle Turkey, Syria, Iran, and Iraq. (Guess which countries in the Middle East are against the Kurds!) They are the main ground force fighting ISIS as the territory they control is right smack dab next to ISIS controlled territory. The US backs them against the protests of Turkey and they are nominally allied to the Iraqi Kurds in the east. The Iraqi Kurds are the ones who actually sent an artillery force to help relieve Kobani a couple years back. The Syrian Kurds are leftist while the Iraqi Kurds are right wing which makes for some tensions but are still united in the idea of a Kurdish state. After ISIS though the Syrian Kurds are opposed to Turkey. The US has been trying to keep Kurdish and Turkish forces apart but once ISIS is gone all bets are off.
US led Coalition
The US led coalition is primarily interested in the defeat of ISIS as a way of keeping them in the Middle East and busy so as not to conduct terror attacks on domestic US soil. They are also against the Assad regime for human rights violations but also to limit Russians and Iranian influence in the Middle East. They try to back the various rebel groups but their support is limited as they are trying to find the ever rarer secular democratic rebel group (there are a few but they are teetering.) Recently, they’ve ended their support of the anti-Assad rebels, causing uncertainty over their role going forward. They are nominally allied with the Gulf States but behind the scenes work at cross purposes in terms of Rebel support but coordinate closely in terms of fighting ISIS.
Finally ISIS. ISIS hates everyone. Everyone hates ISIS. ISIS’s ideology and expression of said ideology puts them at violent odds with literally everything around them that does not adhere to their very specific sub-branch of Wahhabi Islam. As such, they have no real allies or backers on the international scene. Their funding largely comes from the sale of artifacts looted from archaeological sites, crime, and taxes from conquered territories. With the loss of Mosul and other territories, their income has been reduced dramatically in the past year.