If the United States intervenes in the Syrian civil war, as it is now considering doing after more than a year of refusing to become involved, it would mark a major shift but might not end the fighting.

The move towards intervention follows claims of President Bashar al-Assad’s government using of chemical weapons in the country’s stalemated civil war. If proven, the use of chemical weapons would constitute a war crime under international law. In response, the US has gathered a flotilla of ships in the area, capable of launching missile strikes against Syria.

The Assad regime has denied the use of chemical weapons. However, Medecins Sans Frontieres says more than 300 civilian dead and thousands more injured show symptoms of nerve gas poisoning.

US President Barack Obama has said establishing that the Assad regime has used chemical weapons would trigger a response. However, Russia will block international intervention in the UN Security Council. The US and its allies are, therefore, looking beyond the UN for a legal rationale for intervention.

The most likely international response will be through a coalition of countries, probably under the auspices of NATO. Such a justification would employ the language of “responsibility to protect”. Syrian neighbour Turkey, a NATO member, is also likely to join the fray.

Obama had been deeply reluctant to intervene in the Syrian conflict, as anti-Assad forces could lead a sectarian massacre. He is also concerned that radical Islamist fighters could establish a new base in the political vacuum, possibly assuming control of the state. Following the Iraq debacle, Obama will also be aware of the irony and possible deception of becoming involved in a war based on the presence of “weapons of mass destruction”. And, perhaps most critically, Syria’s allies, Russia and Iran, would not only be deeply angered by such intervention but could also become directly involved in the conflict.

With the battling factions being supported by external actors, Syria’s civil war has been, in part, a war by proxy. That proxy war would be extended, with likely greater Saudi support for radical Islamists and, almost inevitably, dragging in neighbouring Lebanon, which in the last few days has been the site of a sectarian bombing believed to have been triggered by the Syrian war.

These outcomes are being factored in to the increasingly likely US-led response. An intervention will probably begin with missile strikes, followed by air attacks and the open provision of weapons to anti-Assad forces. A missile attack would first neutralise the Assad regime’s anti-aircraft capacity, as well as target chemical weapons sites.

A US-led attack could, initially, tip the balance of the war against the Assad regime’s forces. But should this intervention trigger a reaction from the Assad regime’s external backers, the war in Syria is likely to become not just more bloody but perhaps not any closer to a final resolution.

*Professor Damien Kingsbury is director of the Centre for Citizenship, Development and Human Rights at Deakin University