If you want a demonstration of how complex the Syrian conflict is, and how greatly its interpretation varies depending on who’s talking, spend half an hour watching CNN and then switch over to RT, the channel formerly known as Russia Today. “West set to punish chemical attacks”, ran the headline on the CNN at time of writing. “Syria asks UN to immediately investigate three new ‘chemical attacks’ by rebels”, RT was declaring simultaneously.

As most of us have known (and managed to avoid confronting in any meaningful form) for over two years, the situation in Syria has been steadily worsening. Over 100,000 Syrians are estimated to have been killed and more than a million people have become refugees. But the longer the conflict has dragged on, the less straightforward it has seemed. “What began as a popular uprising against an autocratic regime,” wrote Seumas Milne in the Guardian this week, “has long since morphed into a sectarian and regional proxy war”.

The tipping point for western intervention came in the form of an apparent chemical weapons attack in Ghouta, an area close to eastern Damascus, on 21 August. Between 322 and over 1,700 people were killed, depending on whose figures you trust, and Médecins Sans Frontières (MSF) reported receiving patients to hospital with “neurotoxic symptoms”. Unverified video footage, uploaded to YouTube by activists, appeared to show rows of motionless bodies and some convulsing patients.

The use of chemical weapons has not yet officially been confirmed. MSF said that they could not “scientifically confirm the cause” of patients’ symptoms. The Syrian government finally agreed to allow UN weapons inspectors to examine the sites of the attacks on 26 August, five days later, but have, at various points, been obstructive in allowing the inspectors to visit all the key sites, one reason why the investigation is still ongoing.

Chemical weapons usage represents the point at which the US has drawn a “red line”. (This may seem arbitrary, given the efficiency with which citizens can be killed without chemical weaponry, but let’s leave that aside for the moment.) It has been believed for over a year that the Syrian government had chemical weapons capability, particularly after Syrian officials warned in July last year that they would not hesitate to deploy chemical weapons in the event of foreign intervention.

At the time, Damascus said they would never use such weapons against their own people. “Any stock of W.M.D. [Weapons of Mass Destruction] or unconventional weapons that the Syrian Army possesses will never, ever be used against the Syrian people or civilians during this crisis, under any circumstances,” a foreign ministry spokesperson said at the time.

In August, US President Barack Obama warned that the Syrian government’s use of chemical weapons would result in a drastic escalation of western intervention in the Syrian conflict. “We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus,” Obama said.

In other words, Syrian President Bashar al-Assad’s government could not have failed to be aware that the use of chemical weapons would carry severe consequences. And yet, the West maintains, they went ahead and did it anyway. Why would Assad’s forces engage in such deliberately provocative behaviour? “The answer to that question is easy,” wrote Bloomberg columnist Jeffrey Goldberg. “Because Assad believes that no one – not the UN, not President Obama, not other western powers, not the Arab League – will do a damn thing to stop him.”

Certainly Assad has demonstrated himself capable of both a grotesque brutality and an indifference to international opinion before. But other commentators don’t find Goldberg’s assessment adequate. In particular, they point out that Assad had little tactical reason to make use of chemical weaponry at this time because his forces were in a strong position against the rebels.

Milne writes that the Syrian rebels have also been implicated in the past in the use of chemical weapons, and may have had a stronger motivation for their use now. “The rebel camp (and its regional sponsors), which has been trying to engineer a western intervention in the Libya-Kosovo mould for the past two years to tip the military balance, clearly has an interest in that red line being crossed,” Milne suggests.

At the moment there simply doesn’t seem to be enough firm evidence to pin the attack unmistakably on either camp, though many maintain that the initial reluctance of Syrian authorities to show UN weapons inspectors the attack sites reads as extremely suspicious, and indeed it does.

But if Western forces are to launch a military intervention in the next few days, they will be doing so with multiple unknowns on the table. They will also be doing so without a mandate from the UN Security Council, since Russia and China are unlikely to give their approval. The attack will be on shaky ground when it comes to its legality – but that does not seem likely to cool the USA’s jets. A CNN commentator summed up the US approach when he wrote: “‘Strictly legal’ should not be allowed to cancel out a legitimate and necessary course of action, even if international law provides no clear support for intervention on humanitarian grounds.”

Syria is not a major oil supplier. In fact, it hasn’t exported any oil since sanctions were imposed against the Assad regime in late 2011. As such, critics of the US can’t plausibly look to this motive for invasion. Nonetheless, it would certainly suit the US to topple one of Iran’s closest strategic allies. Retired four-star general and the supreme NATO commander during 1999 bombing campaign on Yugoslavia, Wesley Clark, claimed in a 2003 book that the Pentagon had been making preparations to attack Syria since the mid-nineties, along with Iraq, Lebanon, Libya, Iran, Somalia and Sudan.

Obama and US Secretary of State John Kerry have consistently framed their Syrian concerns as humanitarian. These concerns don’t seem to be shared by the majority of the US public, if a Reuters/Ipsos poll is anything to go by. Last Saturday, the percentage of Americans polled who thought Obama should intervene in Syria stood at just 9%, though by Tuesday this had risen to just less than 28%.

Despite the apparent lack of public appetite, western discourse on the matter has been heavily moralistic. But, as writer Brendan O’Neill pointed out, “all the discussion so far has focused, not on the potential moral consequences of bombing Syria, but on the moral needs of those who would do the bombing”. The conversation has frequently been framed as if Syria were nothing more than a kind of moral experiment for Europe and the States, with talk of inaction calling into question the west’s “moral compass”, and Syria’s situation described as “hold[ing] up a mirror to Britain”, and providing “a question mark painted in blood, aimed at the international community”. O’Neill concluded snidely: “They’re so vain, they think someone else’s war is all about them”.

Of course, international wars are always partly about domestic politics, and here, too, it’s clear that many UK and US politicians have one eye on Syria and one eye in the mirror. “Backing action in Syria could give [Labour party leader Ed] Miliband a much-needed injection of gravitas,” wrote respected British political analyst Polly Toynbee on Wednesday. Ask not what we can do for Syria; ask what Syria can do for us.

It’s a sign both of the times, and of the complexity of the Syrian conflict, that more than one British MP has taken to Twitter this week to ask their constituents to help them make their minds up on which way to vote on Syria on Thursday. They should know that there is an awful lot riding on this decision, and a frightening paucity of evidence to base it on. “We’ve seen this movie, we know how it ends,” warned Labour MP Diane Abbott. DM

Read more:

• An attack on Syria will only spread the war and killing, in the Guardian
• What justifies intervening if Syria uses chemical weapons?, on CNN