One misconception about war is that it helps the nation's economy; this is not true. It helps the economy of the companies that supply materials and weapons but is an economic burden on the government and on the taxpayers. Prolonged warfare especially resulting in a loss or perceived loss is one of the preconditions for internal revolution. The Nazis blamed the Weimar Republic for the loss of WWI and in particular Kaiser Wilhelm II and used it to justify their takeover.
(It's a bit misleading as the Weimar Republic did not exist until after WWI, the German states having been designated as the Deutches Reich prior to 1918. Of course after the initiation of the Third Reich blame was shifted to the Jews.)
The point is that a protracted war, especially one that is a loss or no gain can be used as an impetus for revolution. One might consider Vietnam and the conflicts in Afghanistan and Iraq here. The national debt suffers from these conflicts; projecting war and power to the other side of the globe is extremely expensive, a burden that will be carried mostly by the taxpayer.
It is also important to note the loss of life and limb of the veterans. The draft or forced conscription makes the matter worse in the eyes of the populace. The current conflicts used contractors to offset manpower requirements that traditionally would have been filled by draftees.
I think the "War is good for the economy" idea started to fade in the late 20th century.
War has become more efficient.
We no longer have to replace hundreds/thousands of planes and tanks ... and people... to maintain a war.
There is also a much, much smaller deployment and casualty rate now. So it is more "tolerable" (and probably even forgotten) for much of the population.
As you say, it only really benefits military contractors.
So rather than the money cycle reaching the majority of Americans through work salaries, it is coming from the taxpayers and going to the big military suppliers - who then buy the politicians .. and the cycle continues.