The liberal world order isn't dead yet. On Tuesday morning, 4 April, in an attempt to terrorise the Syrian population into submission by, among other things, demonstrating that there was no crime so monumental it would trigger an international response, the regime of Bashar al-Assad deployed nerve agent against the town of Khan Sheikhoun, massacring at least 84 people. A third of them were children.

On the evening of 6 April, President Donald Trump ordered cruise missile strikes that demolished the airbase from which Assad launched this latest atrocity. In doing so, the president has created the space to chart a new way forward after six years of failed Western policy that has led to a humanitarian abomination and a strategic catastrophe threatening the Atlantic Alliance.

In August 2013, Assad murdered 1,400 people in a few hours with the nerve agent sarin. This crossed then-President Barack Obama's "red line" and it appeared that a round of punitive strikes would be directed against the regime. In the course of events, Russia took advantage of Obama's reluctance to provide a fig-leaf so that he would call off the strikes, a "deal" that was supposed to remove Assad's chemical weapons.

This re-legitimised Assad. It made him a partner in disarmament, discrediting rebels aligned with the West and empowering jihadists who fought alongside the revolutionaries and said the West was on Assad's side all along. And, of course, Assad never did disarm: the moment he did, his usefulness was at an end. Meantime, Assad switched to chlorine gas and in December even returned to the use of nerve agents.

Despite the devastating consequences in Syria and the proliferating use of chemical weapons as the international taboo frays, Obama has said he is "very proud" of his stand-down in 2013, and indeed touted his entire Syria policy as the best that could have been done. Obama's National Security Adviser, Susan Rice, defended the 2013 actions as recently as January, saying they had forced the Assad regime to "verifiably give up its chemical weapons stockpile".

Though the White House made this claim of complete disarmament in 2014, it has been clear in open source since mid-2015 and confirmed on-the-record in February 2016 by US intelligence, that Assad had not surrendered all of his chemical munitions.

Given the presence of Russians at the Shayrat base from which Assad launched this week's attack, and the US having good enough intelligence to bomb around both the Russians and the sarin on the base, it suggests that the Obama administration well-knew this, and raises questions about what was done to push Moscow to enforce the deal it had proposed to spare its client retribution for its murderous conduct.

Trump came into office on the back of rhetoric that was noticeably pro-Assad, and on 30 March – just five days before the 4 April attack on Khan Sheikhoun – the US Secretary of State Rex Tillerson and UN ambassador Nikki Haley gave coordinated statements saying that Assad remaining in power was acceptable to the US, since the priority was against Isis.

This was merely a formalisation of Obama's policy, it is true, and the Obama administration had been keen to trap its successor on the course it had laid down. Nonetheless, a public statement from the American government of what has thus far been unspoken is important.

If this was read in Damascus as a green light, it was a terrible miscalculation. Perhaps affronted by such behaviour after this rhetorical concession and evidently keen not to pay the political price of Obama's retreat, President Trump first attempted to go through the United Nations Security Council and found it (again) blocked by Russia. Lamenting that Moscow was either unable or unwilling to restrain its ally, the US acted alone.

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US President Donald Trump delivers a statement about missile strikes on a Syrian airbase at his Mar-a-Lago estate in West Palm Beach Carlos Barria/Reuters

The US Navy launched 59 cruise missiles at the Shayrat base about 1:40am British time. This was within 60 hours of Assad's attack, a marked contrast to 2013, when US allies like France needed (and were prepared for) a lightning strike, for domestic political reasons, and were instead faced with a delayed process, even before the strikes were cancelled.

The Pentagon released details on the flight path taken by the regime plane that used chemical weapons, taking off from Shayrat, which is now in ruins after the first deliberate military action by the US against the Assad regime, crossing the Rubicon of attacking the formally sovereign power in Syria. The US also destroyed nine fighter jets, no small thing with a regime as decrepit as Assad's.

There are two additional factors that make the US attack significant militarily as well as politically.

First, the base was known to house Iran's Islamic Revolutionary Guard Corps (IRGC) and its Lebanese proxy, Hezbollah, the forces that saved Assad in 2013 and have kept him alive ever since. Second, air power has been the regime's key advantage over the rebellion — and its most lethal weapon of indiscriminate murder and displacement. It was from Shayrat that fixed-wing aircraft recently played a key role in turning back an insurgent offensive in Hama.

Trump's brief, impassioned speech afterward explained that he had acted to defend US vital interests by deterring the use and spread of weapons of mass destruction, and to impose a cost on those who cruelly murder civilians, including "beautiful babies".

Obama and his defenders had a habit of portraying the options in Syria as doing nothing to complicate Assad's policy of mass-homicide or an Iraq-style invasion that led to World War Three. In military terms, even after the Russian intervention, this was always untrue, and it is now demonstrable that Moscow's bellicose language in this direction was a bluff.

5 April 2017: US Ambassador to the UN Nikki Haley holds photos of victims of a suspected Syrian chemical attack that killed civilians including children as she speaks at a UN Security Council emergency session Timothy A Clary/AFP

Moscow's statement that its support for Assad was not unconditional almost certainly means that Washington informed the Russians ahead of time that this was coming. Russia's government professed itself "disappointed" this morning and suspended the deconfliction mechanism, which will likely be restored in short order. The Assad regime has laughably claimed that Shayrat was being used for anti-Isis operations and that four children were killed, a lie not unlike that used by Muammar al-Gaddafi in Libya in 1986.

There are risks of counter-escalation in the aftermath of this. Tehran could recommence attacking US forces in Iraq through its Shia militias, and it is also possible that the Iranian proxies and other pro-Assad forces could intervene in the upcoming operation to oust Isis from Raqqa City. But in both cases, it underlines how troublesome it was that the last administration allowed the Iranian revolution to consolidate so much control across the Fertile Crescent.

In the immediate term, these strikes have taken one of the most hideous weapons off the battlefield in Syria and mean that, unlike John Kerry, Tillerson is not addressing the pro-Assad coalition from a position where they know there will be no consequences no matter what they do.

Going forward, Trump has gained himself a store of credibility, at both a popular and governmental level in the region, that will allow him, should he choose to do so, to reset America's heretofore failed policy, that failed to staunch the human carnage within Syria and the spillover that has seeped into Europe, destabilising and radicalising politics there to the advantage of a Kremlin that seeks to break the Transatlantic Alliance.

The monomaniacal focus on Isis has, among other things, led to the US partnering in an unbalanced way with the Kurdish PKK in Syria, severely damaging relations with Nato partner Turkey; assisting the pro-Assad coalition in operations like Palmyra; and enabling the expansion of Iran's power in both Syria and Iraq.

These are not only negative developments in themselves but defeat their own purpose by providing conditions for Isis and al-Qaeda to thrive in. If the focus now turns to containing Tehran and liberating Raqqa in alliance with traditional allies and localist forces, it just might allow the restoration of stability and the sustainable defeat of Isis.