This week’s anniversary of our brief, and widely forgotten, ‘Suez War’ is a timely reminder of the psychological malaise that often afflicts fallen nations. For just as an invalid can refuse to accept the onset of a debilitating condition, overreaching himself to suffer trauma and injury as a result, so too has this country also harboured similarly damaging post-imperial delusions.

This unfortunate state of mind became clear exactly sixty years ago, when the governments of Britain and France launched a daring military venture to seize control of the Suez Canal. At dusk on 31 October, three months after the Egyptian leader Gamal Abdul Nasser had nationalized the Suez Canal Company, British and French planes started to bomb Egyptian airfields. Several days later, on 5 November, the infantry arrived and moved fast to secure control of the Canal.

But despite military successes on the ground, London and Paris were quickly overwhelmed by their political foes abroad. News of the operation provoked a ferocious barrage of criticism from the world over, particularly in the Commonwealth but above all from Washington. A furious President Eisenhower accused Anthony Eden and Guy Mollet not just of duplicity – he had been given no prior notice of the operation – but of driving Egypt and other countries into Soviet hands. He effectively imposed economic sanctions on his two allies, whose leaders aborted the operation and accepted a UN-brokered ceasefire.

The outcome was an outright humiliation for both countries, and their collaborator, Israel. Not only did Nasser remain in control of the Company and the Canal but Britain and France suffered a severe loss of face, forced into surrender by financial pressure, exerted by their closest ally, and by the condemnation of the watching world.

Both countries had paid the price of the clear mismatch between what they wanted to do and what they were capable of. For long imperial decades, Britain and France had been able to invade and occupy foreign lands, just as in 1882 William Gladstone and General Garnet Wolseley had captured Egypt in a matter of weeks. But by 1956 neither country was quite willing to accept that it no longer had the resources to do so and that the United States now called the shots. Instead, Eden had wanted to “destroy Nasser” in the same spirit as an imperialist of a different age.

But decades on, such post-imperial delusions still haunt our imaginations. The British-French assault on Libya in 2011, for example, shared several traits with the ill-fated Suez War. Both ventures suffered from humiliating outcomes – Libya still remains in a state of chaos – and were carried out with a lack of strategy and post-war planning. And, in both cases, the two allies misjudged and exaggerated what their own capabilities.

David Cameron proclaimed that his country has “one of the finest armed services in the world” and is “one of the world’s leading military powers…with a huge strength in diplomacy, soft power and development”. As my new book describes, the 2011 campaign exposed a harsher truth: almost as soon as the war began, it was the Americans- reluctantly dragged into the campaign- who undertook most of the sorties. The British and French carried out the rest but soon ran short of intelligence-gathering aircraft, refueling tankers, precision-guided bombs and ammunition, forcing them to rely even more heavily upon the Americans to finish the job they had started.

By the time NATO formally halted its seven-month bombing campaign, on 31 October, it had long become clear that the cost of the war far exceeded what Britain could afford, particularly at a time of recession: the chancellor George Osborne stated that it cost the Treasury “tens of millions” but the real figure was closer to £320 million. Nor did Britain and France have the resources to rebuild and sustain a post-Gaddafi Libya, even if their leaders had given any forethought about how to do so.

Decades after our ‘retreat from Empire’, the British public and its leaders need to remain vigilant about undertaking similar such ventures and making delusionary assessments about what we remain capable of undertaking in the contemporary world. We need to rely on more cautious judgments, such as those that were put forward in September in a report by the House of Commons’ Select committee. This pointed out that David Cameron and Nicholas Sarkozy could have avoided war by reaching out to Gaddafi and striking a compromise, perhaps by using Tony Blair’s links with the Libyan leader. Comparably, during the Suez crisis only very few members of the governing elites in Paris and London – Jean Monnet, Pierre Mendès France and Walter Monckton – had urged restraint upon their belligerent leaders.

In the same way, we will need to make the most of such peaceful means to avoid foreign wars, pulling strings and striking deals with the same cleverness as our ancestors who managed to ‘divide and rule’ their enemies. As the Syrian crisis continues, we must hope that our new prime minister and her cabinet will recognize their limits.

RT Howard is the author of Power and Glory: France’s Secret Wars with Britain and America 1945-2016