Western powers decide that the ruler of a major Arab state has become an intolerable threat.
By Roger Hardy
BBC News Middle East Analyst
They launch a concerted attack to topple him, but provoke a storm of international controversy over the wisdom - and legality - of their action.
Nasser was regarded as "an intolerable threat"
Half a century on from the Suez crisis, the contemporary echoes are unmistakable.
In 1956 the Western powers were Britain and France. The Arab ruler was President Nasser of Egypt.
Both felt threatened by his dramatic decision to nationalise the company which operated the Suez Canal.
The British Prime Minister, Anthony Eden, regarded the canal as the "jugular" of the British empire.
The French resented the help Nasser was giving the Algerian insurgency.
The two European powers reached a secret agreement with Israel to attack Egypt, regain the canal and overthrow Nasser.
US halted intervention
But it all went disastrously wrong.
The American President, Dwight Eisenhower, was furious with his British ally for keeping him in the dark - and forced the three aggressors to halt their attack and withdraw from Egyptian territory.
Nasser emerged an Arab hero, Eden's career ended in ruins - and the whole affair confirmed the demise of Britain and France as global powers.
Britain and France felt threatened by the nationalisation of the canal
Then and now historians find the comparison between Egypt in 1956 and Iraq in 2003 irresistible - even if the differences are as obvious as the similarities.
Saddam Hussein was no Nasser - however much he would have wished to be.
In the earlier crisis, the United States brought the fighting to a close; in the later one, it was the instigator.
Above all, the international climate was completely different. In the 1950s there were two superpowers locked in a Cold War.
In 2003 America dominated world affairs in an entirely new way.
Was it legal?
Nevertheless both crises raised issues that are uncannily alike.
Was the action of the Western powers legal? In neither case did the argument of self-defence really hold up.
Were they sincere in going to the United Nations in search of a diplomatic solution - or had they already made up their minds to go to war?
In both cases, there is evidence of the latter.
Given that the real aim was "regime change", how far was there a coherent plan for the "day after"?
In 2003, as in 1956, there seems to have been astonishingly little planning for the aftermath.
Finally, how far was public opinion deceived?
This is a sensitive charge. All politicians make mistakes, but mistakes based on deception carry an added stigma.
Suez ruined Eden's career; No final verdict yet on Blair's
Eden kept the truth about Suez not only from the Americans, but from members of his own cabinet.
Certainly today's British prime minister, Tony Blair, would resist any comparison between himself and Eden.
He would say he made an honest mistake in claiming Iraq had weapons of mass destruction.
His critics would say he "spun" the country into a war which achieved "regime change" but with disastrous consequences.
History's judgement on Britain's role over Suez has been damning.
It remains, to this day, a moment of shame - a warning to politicians and generals alike of the price to be paid for risky foreign adventures.
For history's verdict on the Iraq affair, we will have to wait a little longer.