If you’re an imperial power, your troops often end up in places that most of your citizens cannot even find on the map: Mesopotamia for Roman soldiers, for example, or Afghanistan (three times) for the British. It looks foolish, viewed with the long perspective of history, and yet lots of people fall for it in the short run.

The coming week marks the 50th anniversary of the Suez crisis of 1956, when Britain, France and Israel conspired to invade Egypt. That operation took much less time to fall apart than the current Anglo-American invasion of Iraq, which has already lasted more than three years, but the parallels are irresistible.

The British-French-Israeli invasion of Egypt was an instant military success, because at that point Egypt had just emerged from centuries of colonial rule by the Turks and the British. Egypt was utterly incapable of defending itself against countries that had long-range bombers, aircraft carriers and amphibious forces. But what was striking, even then, was the sheer helplessness of the Anglo-French invasion forces once they had won their military victory.

It was one of those "wars of choice" that great powers in decline sometimes fight just to show that they are still top dog. Britain and France had both suffered a sudden, severe demotion in their great-power status after the Second World War, as it became clear that the principal players in the next round of the game were the United States and the Soviet Union, countries of continental scale with which they could not hope to compete. So the declining powers had chosen a war against Egypt as a way of demonstrating that they were still serious players.

It is unlikely that anybody in power in London or in Paris ever put it quite that way at the time. Even in the innermost circles of power, things are rarely called by their proper names, and the lies are layered. Thus the British and French secretly agreed with the Israelis that the latter should invade Egypt, whereupon Britain and France would "intervene" to separate the Israeli and Egyptian combatants and "protect" the Suez Canal.

Behind that was a story about how Egypt’s nationalisation of the Suez Canal was threatening world trade (though Egyptians were running the canal perfectly well), and another story about how the shareholders in the Anglo-French company that had previously run the canal were being victimised (partly true, but hardly a cause for war). And behind all that was the real reason: the existential angst that British and French power in the region was in precipitous decline, and needed a successful war to shore it up.

Fast-forward fifty years to Iraq, and the script has hardly changed. The great power facing demotion now is the United States (as new great powers emerge in Asia), and the target is another Arab country: Iraq. The rhetoric that justifies the invasion follows an American rather than a European model, so there is more emphasis on apocalyptic threats (Saddam Hussein has weapons of mass destruction that he will give to terrorists) and on moral considerations (he tortures and kills people) than in the Suez episode. But behind all that the motive is the same: the need to shore up American power in the Middle East by a successful war against a defiant local ruler.

American power wasn’t actually in rapid decline in the Middle East in 2003, any more than British and French power was in 1956. It was in slow decline, just as British and French power had been in the 1950s. In 1956 the revolt against France in Algeria had barely begun, and Britain still effectively controlled Jordan, Iraq and the Gulf states. The Suez invasion was an unprovoked attack intended to destroy Gamal Abdul Nasser, the charismatic Egyptian leader whom the British and French feared would rally the Arabs against their domination of the region — and it ended by destroying their domination of the region.

The analogy with the current American invasion of Iraq is striking. The United States government offered the same blizzard of lies to justify its invasion of Iraq, and its fundamental goal was identical: to shore up a slowly deteriorating domination of the region by a striking military success. It was another "war of choice" — in cheerleader-journalist Tom Friedman’s famous phrase — and it is coming to the same grim conclusion.

It is taking much longer to reach that conclusion because America, the sole superpower, has nobody else to tell it to stop. US President Dwight Eisenhower did that service for the British and French in 1956, telling them to stop the nonsense at once, and they obeyed. If they had been allowed to continue, as Michael Foot (later a contender for the leadership of the Labour Party in Britain) and Mervyn Jones noted in a book published in 1957, Britain and France would have faced guerilla war in Egypt, and in the end "we would have had to get out again, expelled by the gun of the terrorist."

There was nobody who could tell the US government to stop when the Bush administration decided to invade Iraq, and so American troops in Iraq are living through (or dying in) the same sort of guerilla war that Eisenhower spared the British and French in Egypt fifty years ago by ordering them to stop and go home.