It's sometimes said that Syria is complicated, or at least beset by incoherent alliances. It isn't that complicated if you accept that some of the allies passionately deny they're allied.
Bullshit aside, there are three sides in Syria, each opposing the other two (so, yes, just a little complicated). They are:
1. The rebels, Turkey.
3. Assad, Russia, Iran, the Syrian Kurds (those represented by the PKK affiliate, the YPG), the US, Australia, Canada, the EU, Jordan, plus some less involved parties like Egypt. Were the term not already taken, this group might be called The Coalition.
One of these parties, ISIS, needs no explaining as far as alliances are concerned. ISIS has no allies. As for the rest, explanation is a straightforward matter of ignoring statements and observing actions.
This approach clarifies relations between the rebels and Turkey. Turkey and the Free Syrian Army undertake joint operations in northern Aleppo. Some rebels don't want Turkish troops on Syrian soil, and they sound like they are enemies of Turkey. But even these rebels want and get indirect support from Turkey or via Turkey, so despite the trash talk and occasional confrontations they are pretty much allies.
So most of the explaining has to do with the third group, which developed in the last couple of years, partly as a reaction to the expansion of ISIS.
First, the EU and the US are enemies of Turkey, the NATO link notwithstanding. The US and the EU have never shown the smallest inclination to defend Turkey against Assad or Russia. They have instead protected Turkish expatriates associated with the very serious, very bloody coup attempt of 2016. They have also backed the armed Kurdish insurgency inside Turkey. They do this by supplying large quantities of arms to the insurgents' Syrian affiliate. Like Russia, the US has installed troops to block the expansion of Turkish/rebel operations. In other words if you simply ignore a bunch of verbiage divorced from reality, the active campaign against the Turkish government could hardly be more obvious.
Second, the US is allied with Assad, Russia, and Iran. It bombs ISIS assets engaged in attacking Assad in the Deir Ezzor region. In supporting the Kurdish YPG, it supports a force whose alliance with Assad is day by day establishing itself as an open secret. Moreover the US is dedicated to destroying the only remaining serious armed opposition to Assad, the (anti-ISIS) radical Islamists. Again like Russia, it regularly conducts air strikes against these factions, a practice instituted already years ago. The EU goes along with all of this.*
The motive for supporting Assad is extreme paranoia about association between rebel groups and Al Qaeda. But why the US and the EU support Assad is not at issue here. The point is, they do in fact support him.
Yes, years ago, the US CIA actually armed rebel groups that actually fought Assad. This is very old
restraining their anti-Assad operations as much as possible. Occasionally, especially in the south around Daraa, these groups do attack Assad, but feebly, because always without US and Jordanian backing.. As of about three years ago, US support for these groups, now via the Pentagon, was accorded on condition that these groups cease to rebel - that is, that they fought only ISIS, not Assad. US and Jordanian relations with formerly rebellious 'rebel' groups is now entirely confined to
Since the US is allied with Assad, it is also allied with Russia and Iran. The US and Russia mount air attacks on the very same rebel groups. US operations against these groups are a minor adjunct to very serious régime and Iranian operations against them. The US is also very closely allied with Iran in its Iraqi anti-ISIS campaigns. Again, verbiage to the contrary does nothing to obscure these realities.
Exactly why things have turned out this way is another story. Essentially the US has decided that its allies are the best bet for over-running all of ISIS' holdings. Probably that's correct. However there is no question that by at least one powerful objective measure - civilians killed, tortured, maimed - Assad is not the least but the greatest evil. Many also argue that to prefer this evil, to back yet another pathologically sadistic secularist is, in the medium or long term - hell, in the all-but-extremely-short term - hardly the strategy most likely to blunt anti-Western Islamist extremism. This piece isn't intended to engage in this debate. It just seeks to undermine the pretense that the debate is about something complicated.
* It appears that Trump's missile strike in response to an Assad chemical attack was a momentary outburst of decency, not a policy change. The May 18th strike on a régime/Shia convoy at Tanf was stated to be a ground commander's response to a threat, again, not a change of policy. The US claimed it happened after Russian attempts to dissuade the convoy from its course.