It's certainly true that the rate of profit on new investments goes up when you destroy existing capital stock. In normal times, continuous expansions make bad

It's certainly true that the rate of profit on new investments goes up when you destroy existing capital stock. In normal times, continuous expansions make bad money chase after good, and you need downturns to wipe out the malinvestments. War wipes out both good and bad money alike, so that, very temporarily afterwards, almost all investments are "good money": pick a rebuilding project and invest in it, and it'll probably turn a healthy profit.