In war, things are rarely what they seem.

Back in 2003, in the days leading up to the U.S. invasion of Iraq, the Pentagon adamantly insisted that the war would be a relatively cheap one. Roughly $50 billion is all it would take to rid the world of Saddam Hussein, it said.

We now know this turned out to be the first of many miscalculations. Approaching its fifth year, the war in Iraq has cost American taxpayers nearly $500 billion, according to the non-partisan U.S.-based research group National Priorities Project. That number is growing every day.

But it's still not even close to the true cost of the war. As the invasion's price tag balloons, economists and analysts are examining the entire financial burden of the Iraq campaign, including indirect expenses that Americans will be paying long after the troops come home. What they've come up with is staggering. Calculations by Harvard's Linda Bilmes and Nobel-prize-winning economist Joseph Stiglitz remain most prominent. They determined that, once you factor in things like medical costs for injured troops, higher oil prices and replenishing the military, the war will cost America upwards of $2 trillion. That doesn't include any of the costs incurred by Iraq, or America's coalition partners.

"Would the American people have had a different attitude toward going to war had they known the total cost?" Bilmes and Stiglitz ask in their report. "We might have conducted the war in a manner different from the way we did."

It's hard to comprehend just how much money $2 trillion is. Even Bill Gates, one of the richest people in the world, would marvel at this amount. But, once you begin to look at what that money could buy, the worldwide impact of fighting this largely unpopular war becomes clear.

Consider that, according to sources like Columbia's Jeffrey Sachs, the Worldwatch Institute, and the United Nations, with that same money the world could:

Eliminate extreme poverty around the world (cost $135 billion in the first year, rising to $195 billion by 2015.)

Achieve universal literacy (cost $5 billion a year.)

Immunize every child in the world against deadly diseases (cost $1.3 billion a year.)

Ensure developing countries have enough money to fight the AIDS epidemic (cost $15 billion per year.)

In other words, for a cost of $156.3 billion this year alone – less than a tenth of the total Iraq war budget – we could lift entire countries out of poverty, teach every person in the world to read and write, significantly reduce child mortality, while making huge leaps in the battle against AIDS, saving millions of lives.

Then the remaining money could be put toward the $40 billion to $60 billion annually that the World Bank says is needed to achieve the Millennium Development Goals, established by world leaders in 2000, to tackle everything from gender inequality to environmental sustainability.

The implications of this cannot be underestimated. It means that a better and more just world is far from within reach, if we are willing to shift our priorities.

If America and other nations were to spend as much on peace as they do on war, that would help root out the poverty, hopelessness and anti-Western sentiment that can fuel terrorism – exactly what the Iraq war was supposed to do.

So as candidates spend much of this year vying to be the next U.S. president, what better way to repair its image abroad, tarnished by years of war, than by becoming a leader in global development? It may be too late to turn back the clock to the past and rethink going to war, but it's not too late for the U.S. and other developed countries to invest in the future.

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Craig and Marc Kielburger are children's rights activists and co-founded Free The Children, which is active in the developing world. Online: Craig and Marc Kielburger discuss global issues every Monday in the World & Comment section. Take part in the discussion online at thestar.com/globalvoices.