Name me one credible economist who believes what you have claimed.
A quick search on Internet and I found an interesting thing:
http://image.guardian.co.uk/sys-files/Guardian/documents/2003/01/27/IoD.pdf
Written by Graeme Leach, Chief Economist 2003,
You can look at page 5 table 1 were he is trying to predict the US Economy in 2003 – Illustrative Scenarios of the Iraq war, GDP % change based on shows the range of US GDP growth forecasts depending on alternative military and geo-political developments.
Scenario Stand-off No War --> 2.2% growth
Scenario Capitulation – no war --> 2.5% growth
Scenario Capitulation – short war --> 2.9% growth
The forecast tells that:
"The key messages from Table 1 are:
(1) In economic terms, a short war is better than no war, or no regime change,
because of the removal of uncertainty.
(2) The highest GDP growth scenario has the highest probability.
(3) The lowest GDP growth scenario has the lowest probability."
It might have something to do with Economy? This is what Economist thought was the most likely scenario when US attacked Iraq. As you can see is the growth with a short war higher then without a war. They did not know then that they were quite wrong regarding the short war.
This is only one of many predictions regarding Economy and war written by Economists.