8:45 a.m., Eastern Daylight Time. A crack in the centre of the world. Someone took revenge on America, and America was helpless.

Nothing there will ever be the same again.

A nation at the height of power, peace and prosperity, blessed by every fortune, whose enemies, it seemed, were as harmless as a few far-off fluffy clouds on a blazing blue September day.

A nation that yesterday looked infinitely vulnerable.

It only took a few men who hate America to hijack its own commercial airplanes and turn them into bombs. It only took a few to ram them into America's most potent symbols of financial and military might. America's sense of its own security exploded with those towers in a cloud of smoke and dust.

Americans will never feel quite so safe again. Nor will any of the rest of us, who looked to them to keep us safe, too.

Their defences were completely useless. Their intelligence and security machine, fuelled by billions of dollars and the best high-tech devices ever invented, could not keep the bad guys out. They slipped through with ease, and struck the nation in its heart.

The skyline of the capital of the world has a gaping wound where the towers once stood; a scar that will last forever.

The slaughter of civilians had always happened somewhere else. Now the horror has come home.

Who did these things? All indications point to a sacred jihad from the Middle East. Maybe it was Saddam Hussein, exacting his blood revenge at last. Or Osama bin Laden, the millionaire fanatic who hates America for sending troops to Saudi Arabia during the war in the Persian Gulf, and for supporting Israel. "Blood, blood and destruction, destruction," he commanded in a videotape to his followers last fall. To kill Americans is holy.

Those who are responsible are most likely men from remote desert lands. Men from ancient tribal cultures built on blood and revenge. Men whose unshakable beliefs and implacable hatreds go back many centuries farther than the United States and its young ideas of democracy, pluralism and freedom.

Hard men, who hide out in desert bunkers and turn the instruments of Western technology -- its computers and CD-ROMs and videotapes and airplanes -- against the West. Men capable of flying Boeing 747s with pinpoint, deadly accuracy, and of giving up their lives for the greater glory of Allah, and of murder on a massive scale. Men who've mastered all the modern Western technocratic skills, and who deploy them with the implacable determination of fanatics.

Men whom most Americans, in their innocent and happy secularism, can scarcely comprehend and hardly ever gave a thought since that nearly bloodless cartoon war in the gulf.

That innocence is now gone.

For a decade now, these terrorists have been America's greatest threat. Its military muscle could have obliterated them long ago, but the will was never there. The tradeoffs were judged to be too great. Mr. Hussein and Mr. bin Laden are experts at survival. They are hard to catch, and surround themselves with men armed with guns and rocket launchers. Americans would not have been able to stomach too much loss of life to catch these men and the possibility of failure and political embarrassment was too great.

And no one wanted to create another Islamic martyr.

Everything will change now, will tip and destabilize in ways far beyond knowing.

The Middle East, the world's economy, the American intelligence establishment, its entire defence strategy, the way it fights its foes. Millions of people of Islamic faith unfairly tarnished by the terrorism of a few.

We have ahead the test by fire of a presidency.

We will have agonizing stories of human suffering, too many to bear. We will have the dead, and countless families shattered, and grief and mourning beyond measure.

But the wounds to America, though terrible, are very far from mortal.

"Americans will persevere," said one New York woman yesterday, staring hard into the camera. She had seen people die before her eyes. That was her message to us and to the men who did this.

Shock and disbelief and grief will give way to anger and resolve.

The fanatics and the terrorists will not prevail. The wider Arab world will not rally to support them, and America will not be driven away. Americans will persevere.

But everything has changed, and the world will never go back to the way it used to be, before the madness began, at 8:45 a.m. Eastern Daylight Time.