The most immediate problem will be the care of hundreds of thousands of refugees, writes Denis Staunton in Brussels
As the likelihood of war in Iraq draws closer, governments and international organisations are struggling to estimate the economic cost of military action and the price of rebuilding Iraq in its aftermath.
Much depends on the duration of any war, the extent of the damage caused to infrastructure, schools, hospitals and other public buildings and the number of people displaced from their homes.
The most immediate problem will be the care of hundreds of thousands - possibly millions - of refugees who are likely to flee to neighbouring countries once war begins. Humanitarian aid would also be needed to tend to the sick and wounded after a conflict.
In Bosnia during the 1990's, care for refugees cost an average of €500 per person per year. If one million Iraqis need such care for two years, the cost would be €1 billion.
To avoid the risk of civil war between Iraq's Shia, Sunni and Kurdish groups, a large peacekeeping presence would be necessary after a conflict ends.
In Bosnia, which is one eighth of the size of Iraq with one sixth of its population, NATO deployed 50,000 peacekeeping troops at a cost of at least €10 billion a year. Seven years later, 12,000 peacekeepers remain in Bosnia.
Some US military planners have suggested that a peacekeeping force of 75,000 soldiers would be adequate in the aftermath of a war with Iraq.
Other US planners have spoken of a 200,000-strong force.
The US Congressional Budget Office estimates that such a peacekeeping force would cost between €17 billion and €47 billion a year, depending on its size - about €250,000 for each peacekeeper. It is impossible to predict the duration of a post-war peacekeeping operation in Iraq but most experts agree that it is likely to be in place for at least five years.
In October 2002, President George W Bush promised the people of Iraq that, once Saddam Hussein was overthrown, they would share in the "progress and prosperity" of our time. "If military action is necessary, the United States and our allies will help the Iraqi people rebuild their economy, and create the institutions of liberty in a unified Iraq at peace with its neighbours," he said.
Such nation building is not only difficult and slow, it is very expensive. It means establishing political, military and security structures, training police and judges and facilitating the emergence of civil society by helping a free media to survive.
In 2001 alone, the European Commission spent more than €100 million on such projects in Bosnia and the cost of similar activity in Iraq is likely to be much greater.
The United Nations estimated in 1991 that it would cost €22 billion to restore Iraq's infrastructure to its condition before the first Gulf War. Economists suggest that this figure may now have risen above €30 billion in view of the deterioration that has taken place since then.
The World Bank estimates that rebuilding in places such as Bosnia and East Timor costs about €1,000 per inhabitant, producing a total for Iraq of about €23 billion.
Some US officials have suggested that Iraq's oil revenues could help to pay for post-war reconstruction. But in a study of the cost of war with Iraq, William Nordhaus, professor of economics at Yale University, argues that such hopes are misplaced.
Even if Iraq increases its production to 3 million barrels per day, it would earn only €25 billion - or €1,000 for each citizen - a year. Much of this would be needed for domestic fuel use and the import of food and medicine.
Moreover, Iraq is burdened by almost €100 billion in foreign debt and many of its business creditors are becoming impatient. So the bulk of the cost of rebuilding Iraq will fall on the US and its allies.