Sophisticated munitions, combat intensity and the high cost of an all-volunteer Army have already made the Iraq war an expensive conflict. With an additional $25 billion, the war's total cost exceeds the inflation-adjusted costs of the Revolutionary War, the War of 1812, the Mexican-American War, the Spanish-American War and the Persian Gulf War combined, according to a war cost study by Yale University economist William D. Nordhaus.
At $174 billion, the Iraq conflict would be approaching the inflation-adjusted, $199 billion cost of World War I, a level the war will likely pass next year.
I presume he means the US cost of WW I, not the cost of all participants?
Impressive numbers, but the relevant number is percentage of GNP. I think that's still a relatively small number, though growing.