This is, without doubt, a defining moment in world history. In declaring this unjustified war on Iraq without any backing from the United Nations, and in the teeth of opposition from many governments and people everywhere, the US government has introduced a new era in international relations. We are now in a phase characterised by aggressive unilateralism on the part of the world's only superpower. The Bush administration has made it clear that, from now on, none of the earlier norms and even institutions that have governed international relations are valid, and that we are back in a situation of the law of the jungle.

Of course, many observers had seen this coming for some time. In a way, the current war is only the practical application of a doctrine that was already spelt out some months ago. On September 17, 2002 the Bush administration published its "National Security Strategy of the United States of America." This extraordinary document, which has been inadequately discussed in the international media, is a declaration of unilateral imperialism.

It asserts that the United States has the right to use military force anywhere in the world, at any time it chooses, against any country it believes to be, or it believes may at some point become, a threat to American interests. This is a claim that has not been made openly by any other country in modern history, even Hitler's Germany. The Bush administration declared strategy paper therefore openly declares its right to bomb, invade and destroy whatever country it chooses.

The document refuses to respect as a matter of international law the sovereignty of any other country, and reserves the right to get rid of any regime, in any part of the world, that is, appears to be, or might some day become, hostile to what the United States considers to be its vital interests. This suggests that wars against small and relatively defenseless states, such as that on Iraq, will be just the starting point for a series of military onslaughts against what may be more formidable targets.

Indeed, now that the aggression against Iraq is under way, people within the US establishment are already talking about the next targets, the most widely mentioned one being Iran, which is suddenly declared to possess "weapons of mass destruction". Interestingly, North Korea, which should be the more obvious target because of its own declaration regarding nuclear weapons, has been relegated to a lower position in the queue of countries requiring US military intervention.

But this open military intervention is only the most blatant and extreme form of US unilateralism which has become ever more evident in the past two years. In many other spheres, the US government has effectively abandoned any attempt to fulfil its responsibilities as world leader, and even any gesture towards maintaining some sense of a community of nations.

It is not just that the United States, as leader of the international capitalist system, has become increasingly incapable of imparting sustained positive stimulus to the world economy. It is also that this case of imperialist over-extension is just the latest in the growing collection of instances that reveal that the US administration is not even willing to try to fulfill its responsibilities as a world leader either politically or economically.

Even the mainstream US economist Paul Krugman, writing as a columnist in the New York Times of 18 March, accepted this point. "The Bush administration has made it clear, over and over again, that it doesn't play by the rules. Remember: this administration told Europe to take a hike on global warming, told Russia to take a hike on missile defense, told developing countries to take a hike on trade in lifesaving pharmaceuticals, told Mexico to take a hike on immigration, mortally insulted the Turks and pulled out of the International Criminal Court — all in just two years."

Of course, this declaration of war on Iraq goes far beyond all that. At one stroke, the United States government has declared its contempt for international public opinion and for the dissent expressed even within in its own borders. Even more significantly, it has announced its contempt for the United Nations and existing structures of international law. It has effectively declared the death of multilateralism, which has huge implications not only for geopolitics, but also for the world economy, which is increasingly based on the framework provided by multilateral institutions like the World Trade Organisation.

It has created – through the aggressive manipulation of the governments of Britain, Spain and Italy - such serious rifts within the European Union that the very existence of that Union may be threatened.  So far-reaching are the myriad implications for the structures that currently allow the capitalist world economy to function, that it is not surprising that so many mainstream and establishment analysts are deeply worried about this act of military aggression.

Now that this unjust war is effectively under way, it is worth considering how significant it is, and how it is likely to rewrite the geopolitical, and even economic, map of the world. The medium-term aim of the United States - to establish control of the oil reserves of this Middle Eastern belt - may appear to be served by this war, but the subsequent reality may become far more complex than the US administration seems to realise at the moment.

The immediate – and most awful – impact is obviously upon the people of Iraq, who are likely to suffer beyond description, well beyond even the extent indicated by the numbers of innocent people dead and wounded through bombing. There are going to be other humanitarian disasters on a huge scale. War would cause chaos to domestic transport, fuel and energy supplies in Iraq, and severely disrupt the existing food ration system.

The United Nations sanctions over the past 12 years have meant that 60 percent of the Iraq population is dependent upon the government for food aid. Even the international aid agencies have declared that these people would immediately "face hunger, if not starvation" in the event of war. Distribution of food aid via the 45,000 outlets across Iraq would almost certainly grind to a halt, especially as UN officials have been withdrawn in advance of the bombing. Although the Iraqi government doubled food rations last month, aid agencies say poverty has meant many of the poorest families have already sold some of it.

Furthermore, about 90 percent of Iraq's sewage treatment stations are vulnerable if power stations are bombed and the electricity goes down. This would lead to polluted drinking water and dire public health consequences, quite apart from the direct fatalities. If military action goes ahead, in addition to immediate food shortages, it is estimated that 39 percent of the population will have no access to clean water, and 5 million will lack access to health care.

Already, because of the 1991 war and UN sanctions, chronic malnutrition among children under five years has soared from 18.7 percent in 1991 to 30 percent in 2000 and infant mortality has risen by 166 percent. One-third of all children no longer attend school, while half a million children are estimated to have died because of lack of medicines due to sanctions.

Of course, the US administration has not been particularly bothered about all these effects, just as it has not spared much concern or resources towards dealing with the problem of refugees that will soon enter Iraq's neighbouring countries, and has not even yet calculated the potential costs of reconstruction in Iraq after all the war damage.

But there are other ripple effects that the US government will not be able to ignore for very long. The more obvious ones have already been repeatedly mentioned: the popular turmoil and unrest, especially in Arab nations, which may end in destabilising existing US-propped regimes in the region; the likely increase in terrorism as a response to such blatant and unjustified violence; the weakening or even collapse of multilateral institutions that the United States has hitherto used to further its own interests.

In addition to these, there are effects directly upon the US economy, which the Bush administration does not even seem to be adequately aware of. The United States economy requires around $400 billion a year of foreign investment inflows simply to cover its trade deficit. Without such inflow, the dollar will plunge in international currency markets, with many other effects. There are already signs that the flow of foreign investment is drying up, and the dollar has been weak in recent months. Yet it is precisely at this time that the US government seems ready to embark upon a whole series of wars against anyone it decides is a present or future threat.

Meanwhile, across the world, peoples' protests against this appalling war continue: marches, demonstrations, sit-ins, candlelight vigils, workers' strikes, peoples' conventions in every corner of the globe. More people have been mobilised in recent weeks for this one issue than any other issue in modern history.  Never before have the people of the world been so united in their opposition to this blatant and aggressive display of force against a people helpless to protect themselves against the onslaught.

Clearly, therefore, the moral battle has already been lost by United States imperialism. And with it, the relatively brief period of ideological supremacy of capitalism is also likely to come to an end. In a peculiar way, therefore, this war may mark the beginning of the end not only for US imperialism but also for capitalism as we know it. The problem is that the transition to anything different will be both long and painful for most people in the world.