There was rejoicing in Tokyo the first day of the Pacific war, and few Americans can be unaware that brave beginnings do not ensure happy endings.

There are still a million armed men in Iraq and you can't count on them to throw down their arms merely because their homeland is assaulted with unparalleled fury.

The war may be long and bloody, and it will be astonishing if it does not bring a few dreadful surprises before victory is gained.

But when the first plane took off for Baghdad the die was cast. There was no longer any profit or any point in protest against violence. Those who have been shocked at American bungling just here and just there in the months before war began now have to ask themselves what other sane course remains but to win the war as quickly as possible with as little damage as possible to American institutions.

The president can claim rightly that Iraq began the violence, that the world community condemned it and authorized counter-violence to end it. Congress approved the use of American troops and so do the majority of Americans.

Whatever the president's errors have been, there will be time later to examine them in exquisite detail, but not now. One urgent business after the war will be to make certain the Congress does not merely rubber-stamp a war after one man has made it inevitable.

Nobody can say the president is incorrect in his central assumption, not articulated well, that Iraq cannot be allowed to dominate and dictate to a great region in which so much of the world's oil is to be found. Nobody can be sure that a different decision by the president -- to continue the sanctions indefinitely -- would have been wiser. It might have proved far more costly in the long run. Any course after September was full of risk. Nobody could know the truly best way to go.

It is insane to think now of undoing all that has been done. It is not possible.

With luck the war will be won in a matter of months.

But beyond that, when peace is established, there will be the problem -- or at least there has always been the problem in the past -- that there is no end to the lust for power. Great empires itch to be greater empires. The very rich are on fire for greater riches.

In America we say we are not an empire. We have no territorial designs. We are good folk here, meaning no harm to man or beast. We trust, naturally, that we shall not hear any smartass opposition from Latin America, Israel, Europe, Africa or any of those "nasty little regimes" that Sen. Daniel Patrick Moynihan (D-N.Y.) spoke of on the Senate floor.

The two adjectives may not have been the zenith of tact on the eve of our ferocious commitment to one of the nasty little regimes, but apart from the rude language virtually everybody agrees with him. Even the most phlegmatic and complacent American, who never had the least doubt that all matters of force could be accomplished in a week or so, must be annoyed that a country as small and in some ways inconsequential should have roused us to such inconvenience.

In ancient Athens at the height of her power, which rested largely on the navy, it was a shock that the sea campaign against Sicily failed. And things went so swimmingly for the Germans as they sailed through Poland that they must have felt cheated by fate at the last.

The usual course of power is to expand until it goes too far and comes crashing down, a phenomenon noticed by the main Greek historian more than 2,000 years ago.

Already in America we have the national assumption, so deep that nobody needs to speak of it, that the world should defer to us. (And long may the world do so, I say.)

But it will never work in the long run. Even as a schoolboy I never admired Pericles as much as I was supposed to. He presided over Athens at the peak of her glory, but he also wrecked the defensive league dominated by Athens (he left it a city of marble, playing loose with league funds). But he was wise in many ways for all that.

You needn't expect, he told his fellow Athenians, that subject people will love you. You now have a great empire and you may say, if you like, it was wrongly acquired. But it is extremely dangerous now to let loose of it.

Many a great state has found itself in this situation. Bit by bit, ruse by ruse, they came to dominance. But there were too many moving parts to hold it all together.

If the countries of the United Nations had enough sense to lay true foundations for a peace-keeping force, to which members contributed in fair proportion, even then the coalition might fall apart when one great state with veto power refused to go along.

But it would be a better chance than leaving the whole decision to the superpower of the moment. A force of all nations will come about when disasters are deep enough to persuade even the great powers that that is the only way to go in the long run.