In Book I of Thucydides’ history Pericles outlines the limitations of the Peloponnesian adversaries. They had no capital. Unlike the Spartiates, most of the allies in the Peloponnesian coalition were agrarians who needed to farm at precisely the time it was best to fight. In contrast, Athens was a sophisticated polis with vast sums of coinage in both circulation and as specie on reserve. Pericles’ adversary, King Archidamus of Sparta, agreed, and so warned his rural Peloponnesians that they were not equipped to fight a long, multifaceted war with even a seasonal militia. This new conflict, he warned, was quite different: “War is not so much a matter of men as of monetary expense.” He proved absolutely right.
The great irony of the war was that the very requisites for victory—an enormous fleet, money for rowers’ pay, and officers deployed overseas for long periods of imperial service—were inimical to the historic assumptions of rural and isolated Sparta, which heretofore had had no monetary economy. Persia finally filled the void, gave Spartan generals untold amounts of gold, and made up losses in men and materiel almost immediately. As long as Greeks were killing Greeks, the satraps of the Persian Empire were happy to subsidize the carnage.
Yet in the war’s aftermath, with the Persian subsidies gone, the implosion of the Spartan empire was directly attributable to its new financial responsibilities of administering a fleet and distant subject states that were so at odds with its old insular moral code. Money and manpower, not always just courage and class, quite literally won wars. The Peloponnesian War offered another bitter lesson, one that would also arise during the transition of Rome from republic to empire. Consensual government started in Greece as a limited enterprise. These constitutional states were predicated on a civic militia cloaked in amateurism and localism, and determined to protect the property of a minority of its citizens. But as the invective of Athenian conservatives from Plato to Aristotle illustrated, war over decades and across thousands of miles required mobilization, weaponry, and capital—and only the new resources of a more centralized and powerful state could meet those vast burdens.
— Victor Davis Hanson, A War Like No Other, pp. 303-304
Emphasis mine.