The strength of a nation can decline as its wealth rises:
Never, perhaps, was the decline of a nation’s strength coincident with the increase of its wealth (using “wealth” not in its primary sense of “weal” or “wellbeing,” but in its now usual sense of “riches”) more signally exemplified than in the case of Athens. As the power of Athens extended, and brought tribute from her subject States, the Athenians thus obtained the means of living without labour, and of amusing themselves with poets, painters, sculptors, and orators.The same thing happens, indeed, more or less in the case of every State, as its revenue becomes great. Those who enjoy its revenues become rich, and can afford to devote themselves wholly to amusement. But the result, when those who, in the capacity of sovereign, divide the revenue among them constitute the whole nation, as at Athens, has the effect of making the whole nation averse to labour, and, it would seem, also averse to danger.
To use the illustration of Socrates, they are crammed with ports, and docks, and fortifications, and revenues, till they are in a state of bloated repletion, and are neither so healthy nor so strong as when they had no foreign revenues, and a small town so unfortified that they considered it indefensible against the host of the Persians. The result, according to the testimony of Plato, who had the best means of being well-informed on the matter, was to make the Athenians idlers and cowards.