Writing in these pages in early 2008, we put the total cost to the United States of the Iraq war at $3 trillion. This price tag dwarfed previous estimates, including the Bush administration's 2003 projections of a $50 billion to $60 billion war. But today, as the United States ends combat in Iraq, it appears that our $3 trillion estimate (which accounted for both government expenses and the war's broader impact on the U.S. economy) was, if anything, too low. For example, the cost of diagnosing, treating and compensating disabled veterans has proved higher than we expected. Moreover, two years on, it has become clear to us that our estimate did not capture what may have been the conflict's most sobering expenses: those in the category of might have beens," or what economists call opportunity costs. For instance, many have wondered aloud whether, absent the Iraq invasion, we would still be stuck in Afghanistan. And this is not the only "what if" worth contemplating. We might also ask: If not for the war in Iraq, would oil prices have risen so rapidly? Would the federal debt be so high? Would the economic crisis have been so severe? The answer to all four of these questions is probably no.