The game is up. Britain has reached the end of a long arc of delusion. For half a century and more it has clung tenaciously to the notion that it was among the pivotal custodians of global order. No longer.

When the Westminster parliament voted this week against joining a US-led military strike against Bashar al-Assad’s regime in Syria it shrugged off the last pretensions of empire.

The journey began nearly 60 years ago with the humiliation of Anthony Eden’s government at Suez. Forced into ignominious retreat by Dwight Eisenhower’s White House, Britain decided that henceforth it would tuck itself in behind the Americans. It could play Greece to Washington’s Rome – a pocket superpower if no longer one of the great powers.

This was the reasoning that saw Britain twice go to war in Iraq, and then rush to take on the Taliban in Afghanistan’s Helmand province. It explains why David Cameron, prime minister, was so eager to join President Barack Obama in punishing the Assad regime for its use of chemical weapons. A majority of MPs thought otherwise. Catching the mood of the country, Conservative rebels joined the Labour party to vote down the prime minister.

True, there was accident as well as historical inevitability in the precise circumstances of Mr Cameron’s defeat in the House of Commons. Puffed up by his transatlantic telephone calls with Mr Obama (one of them lasted a full 40 minutes, Downing Street announced breathlessly), the prime minister had been characteristically lazy in his preparations.

Never mind that UN weapons inspectors were still on the ground or that there had been no real discussion in the UN Security Council. Mr Cameron is nothing if not self-confident. He would busk it – call back MPs from the summer recess and cajole and charm them into backing the dispatch of British forces to punish the Syrian tyrant.

The prime minister has never had much time for strategy, but this time he was more than careless. Ed Miliband’s decision to lead the Labour opposition into the No lobby may well have been as much about party politics as high principle, but Mr Cameron’s cavalier disdain for diplomatic process had given him all the cover he needed.

Just as Americans have tired of fighting unwinnable wars in the Middle East, so the Brits have decided to count the cost of their pretensions. Much was said during the parliamentary debate about the shadow cast by Tony Blair’s decision to join George W Bush in toppling Saddam Hussein. Dodgy intelligence dossiers and the absence of weapons of mass destruction have certainly taken their toll on trust. So did the British army’s hasty retreat from Basra as post-Saddam Iraq fell to civil war.

There was more to it. This week’s vote gave voice to a deeper weariness – a public mood that, albeit in sometimes inchoate form, reflects the harsh reality of British power. The war in Afghanistan, where the army has taken much heavier casualties than in Iraq, is a big part of the explanation. After more that a decade of fighting the Taliban, next year’s planned withdrawal is an admission of defeat. All that blood and treasure, and, voters ask, for what?

The war in Libya scarcely changed the calculus. Mr Cameron and Nicolas Sarkozy, then French president, had their moment in the sun after the fall of Muammer Gaddafi, but the country has since fallen into violent chaos. Much of Benghazi, the stage of the Franco-British triumph, now belongs to affiliates of al-Qaeda.

One curiosity in all this is that even Mr Cameron seems to have accepted the limitations on British military reach. His government’s austerity programme has included deep cuts in the defence budget. Capabilities have been hollowed out and capabilities cut. I recall a conversation with a senior US official when Mr Cameron was leading the clamour for intervention in Libya. The official remarked that if the prime minister wanted to indulge in sabre-rattling he should make sure he had his own sabre. “Hasn’t he just abolished your army?”

I doubt that the vote will see Mr Obama rage at British perfidy. Any British contribution to strikes against Syria would have been more about political solidarity than military punch. If the president decides to strike at Mr Assad’s command and control, and other military centres, he has plenty of his own cruise missiles at hand.

His many troubles with the Congress will also have taught Mr Obama about the uncomfortable political realities of democratic systems. Yet this week’s events will have an impact. They will strengthen a rising US perception that Britain is an ally pulling back from the world. Mr Cameron’s decision to call a referendum on EU membership fits this picture. Why would Britain weaken itself further by disengaging from Europe?

There lies the danger. It is one thing for Britain to confront reality. In its own way, the US has been doing the same by rationing its interventions in the Middle East. But, even as a diminished power, Britain still has something worthwhile to offer in helping to sustain global order.

There were good arguments for, as well as against, acting to deter Mr Assad’s regime from using chemical weapons. For all the cuts, Britain still has a sizeable military, a first-rate diplomatic service and a permanent seat on the UN Security Council. To leave behind the delusions that were the legacy of empire should not be to pull up the drawbridge against a dangerous world.

philip.stephens@ft.com

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