Sparta is the closest example i think of. all the men were soldiers and all the hard labor/farming were done by slaves/healots. eventually led to technological stagnation & societal collapse
Did Sparta actually fall because Thebes out innovated them on the battlefield?
If so, perhaps an argument _for_ the military industrial complex as a nation’s savior.
Perhaps you are thinking of classical Athens, and its loss to the Greek city-state of Syracuse in Sicily?