By far the best outcome of the Iraq crisis would, of course, be a peaceful withdrawal of Saddam Hussein to exile or his overthrow by his own army in the next few days. That would ex post facto justify the US-British threat of war, writes Garret FitzGerald.
The crisis would then evaporate, although some bitterness would remain between the major powers, the US and Britain on one side and France and, to a lesser extent, Germany on the other. The impact on US and British relations with Russia and China might be less serious.
Next to that, the least bad outcome would be a short war with limited, mainly military, casualties.
However, even that could have a number of negative consequences. If the occupying forces failed to find any of the mass destruction weapons they confidently claim exist, the credibility of Britain as well the US would be gravely damaged, regardless of how well-received the occupying force might be by various groups of Iraqis.
For it is the weapons issue that is the purported justification for the war - not regime change which, in the absence of an immediate humanitarian crisis such as in Kosovo, cannot justify armed action against a sovereign state.
Clearly, if after such a war a genuine discovery of mass destruction weapons did occur, that would offer a measure of retrospective justification for the invasion, but there would still be fears that this outcome would encourage the US further to exert its power unilaterally and arbitrarily throughout the world.
Moreover, no such retrospective justification could undo the damage done to the fragile role of the United Nations in helping to preserve peace throughout the world.
Furthermore, it will not have been helpful to international relations for anti-American feeling worldwide to have been reinforced among a majority of the population of very many countries.
There must also be doubts about the US insistence on installing an American military regime in Iraq after the war has been won.
Conscious of its own lack of success in peacekeeping, e.g. Somalia, and of its inexperience in governance abroad, as well as perhaps of cost factors, in post-war Afghanistan the US was quick to hand over to other states the job of helping the country back on to its feet.
US generals tend to be very protective of their troops and intolerant of having their authority challenged, and how they will cope with the task of civil administration of a country like Iraq must be a matter of some uncertainty,
There must also be particular concern at the US proposal that in Kurdish northern Iraq the Turkish army be allowed to take control.
Thus even the second-best outcome, a short war that was not too costly in human terms and that secured a positive initial response from the peoples of Iraq, has a considerable potential downside.
Beyond all that, there is the further danger that this war might de-stabilise other parts of the Middle East such as Saudi Arabia. The removal of that repressive regime by revolution in these circumstances would not necessarily lead to democratic government. A fundamentalist takeover would seem more likely - which would not bode well either for human rights in that country - or for our oil supplies.
There must also be a danger that large-scale US military involvement in Iraq might tempt North Korea to an aggressive course of action, with all the dangers of a nuclear conflagration that could entail, or, less probably, tempt India or Pakistan to war while the US cat was engaged elsewhere.
Finally, a war in Iraq, whatever its outcome, must encourage al-Qaeda to new monstrosities.
To sum up, it is hard to see much good coming of an Iraq war, but one can readily envisage it generating a lot of evil.
The impact of this war upon Britain is much debated. If it is short and not too lethal for invader and inhabitants alike, and if the occupiers are welcomed by most Iraqis, Tony Blair may survive in the short run at least, although his longer-term future will remain in doubt. Even a "successful" war will not assuage the anger he has aroused on his own back benches.
We in Ireland must hope that he will at any rate survive long enough, and strong enough, to put finally to bed the Belfast Agreement, the negotiation of which will always be seen as one of his greatest achievements.
In our own State, the indications are that the Government is confident enough of its party support to ignore popular pressure to withdraw the Shannon Airport facilities in the case of a war lacking UN authorisation.
Concern to maintain US government support for our peace process, as well as fear of possibly alienating sentiment among the largely republican industrial community in the US that has been responsible for so much of our economic prosperity, look like submerging any ethical concerns about US actions.
In this connection the evident enthusiasm with which our anti-American lobby has latched on to this Shannon Airport issue may have obscured the more significant shift of wider Irish public opinion, normally well disposed towards the United States, against US unilateralism.
The reality is that Europeans generally, and Irish people in particular, have become attached to peace and have become hostile to war as an instrument of policy. In this, many Americans are clearly differentiated from most Europeans, for much of the United States seems to be living still in an older world where force was a fairly acceptable option - force that for us has become the very last resort.
This gulf between prevailing European and American attitudes to violent action, which is also very apparent in relation to capital punishment, has been growing silently throughout the decades since the second World War, but has been suddenly exposed by the present crisis.
However, this crisis has also divided Europe's governments in a very damaging way. Differences between Britain and its major European partners, France and Germany, have been seriously exacerbated. All in all, we are bound to be left with a very messy situation.