Forty percent of the entire U.S. GNP was directly related to the war effort by 1943. There were other structural differences as well. For example, the collection of things such as metal products for manufacturing which were collected by everyone from individuals to corporations and used for steel-making without any financial transaction. There was significant rationing on many essential materials, and strict wage and price controls were in effect to control inflation. There was also massive amounts of unpaid overtime given by workers in all sectors of the war economy. There were also immense volunteer efforts where time was given without pay solely because of the war. Wartime transfers and allocations of land, labour and goods were priced differently during wartime than they would have been during peace time.
There are many others.
It's also worth noting that the figures for the cost of the Iraq war that are being quoted range from about two trillion to three trillion dollars. That's a pretty significant difference in the estimates.