NEW YORK – With March 20 marking the fifth anniversary of the United States-led invasion of Iraq, it’s time to take stock of what has happened. In our new book The Three Trillion Dollar War , Harvard’s Linda Bilmes and I conservatively estimate the economic cost of the war to the US to be $3 trillion, and the costs to the rest of the world to be another $3 trillion – far higher than the Bush administration’s estimates before the war.