Mike Anderson has written a very interesting article about the Spartan army after the Peloponnesean war, with that invaluable thing, numbers attached.
At the end of the war, by 398 BC, the Spartans could field 6,000 hoplites – Spartiates, who lived as permanent soldiers and ate in the communal messes, under their peculiar but egalitarian polity. But the loot of the war wrecked the state. Once there was money, there were rich and poor. Rich men are not keen to live as conscripts, and their sons less so.
Famously the Spartan ascendancy came to an end at the battle of Leuctra in 371, when they were defeated by the Thebans under Epaminondas. The result of the battle was met with general rejoicing among the Greeks. But Mike points out that only 1,050 Spartiates were present. The rest of the army was made up of Perioeci, the associates. Luxury had destroyed the Spartan system; new methods of fighting did the rest.