By John Simpson The BBC's world affairs editor

With hindsight, an American invasion of Iraq was always inevitable.

President George W Bush was half-disposed towards it when he came into office at the start of 2001.

The attacks of 11 September made it a certainty.

People who are against the war tend to say it is all about getting hold of Iraqi oil, or it is all about asserting America's position in the world.

Or they will say it is all about sorting out Israel's enemies at Israel's behest, or attempting to get a democratic Middle East.

Or it is all about doing what Mr Bush's father failed to do, and win a second term.

It is not just about any single one of these things. It is about all of them.

Weapons

Different senior members of the Bush administration believe that one or more of the items on this list of factors is essential to America's political or business interests.

If you tot them all up, it is impossible to believe Mr Bush would do anything else.

KEY DATES

31 Jan - Bush meets Blair 5 Feb - Powell to address UN Security Council 14 Feb - Further report from weapons inspectors 27 Mar - Blix submits new report to UN

Next steps in full

There was only one faint possibility of avoiding war: If President Saddam Hussein convinced the rest of the world he had genuinely given up all his ambition to make Iraq the dominant military force in the region by means of deploying chemical, biological and nuclear weapons.

It would have been hard even for the United States in its present mood to attack a country which was manifestly innocent.

UN vote

There is no doubt whatever that Iraq did its utmost to present itself as entirely clean.

Persistent reports from senior Arab sources, as well as more recently from Israel, have claimed that Egypt and other countries helped Iraq to dismantle its arsenal during the four years after the last group of UN weapons inspectors left the country in 1998.

If that is true - and the Egyptians have denied it angrily - the process simply was not enough.

When Hans Blix, the head of the inspection effort, reported to the UN on Monday, it was clear his team had serious doubts about the genuineness of Iraq's effort to clear out its weapons.

By that stage, all the opponents of war could do was argue for the inspection process to continue.

But President Bush is determined now to go ahead. And given America's power and influence nowadays, the UN will almost certainly vote to let him do it.

Panorama: Tackling Saddam was broadcast on Sunday, 2 February 2003, at 22:15 GMT on BBC One.