Someone summoned me ?
Before we talk empire and Greece we have to look at demographics :
- Thebes never managed to dominate outside of Boeotia, even under Epaminondas when they beat the Spartans : they first managed to gain their autonomy thanks to Athens' support, and then had only a decade of relative dominance thanks to a pair of victories that bled Sparta dry. While Thebes could have relatively powerful forces for the time (in the 10 000 hoplites range), it had little ways to project them away. Once again the period of Epaminondas is an exception, as he was able to go as far as Sparta itself, but the rest of the time they do not manage to send their men outside of Boeotia.
- Corinth had a fleet and managed to create a large number of colonies but its situation in the bottom of two gulfs meant it was easily isolated from its foundations, as proven by the athenian colony at Naupacte for the western side, and the inability of Corinth to challenge Athens at sea in the Egean. Its population was in fact rather limited and a lot of its men were at sea, leaving it with relatively little land forces to defend itself. Thus it always depended on Sparta for its land defense. Its financial revenues, while impressive, were also far inferior to Athens' who had the silver mines of the Laurion to finance its forces, especially its navy. If I recall properly the ship building rate was 1 in Corinth for close to 10 in Athens... Corinth had no chance.
- Argos was a good contender for a Peloponnesian hegemony, with large infantry forces in the 6th and 5th centuries, but here too we are in the 10 000 men range. And they never managed to beat Sparta, even with the aid of the Athenians : they remained confined to their plains of north-east Peloponesus. It would then be overshadowed by other Peloponesian cities, more to the west and south, such as Megalopolis and Messene, cities that were also part of leagues in ways that Argos never managed to create due to its agressive stance against many of its neighbours.
- Sparta : its political system was too restrictive for the demographics to grow in ways allowing empire, and also to actually manage an empire. Agesilaos campaigns' in Asia Minor are a good exemple of that. Add to that the need to keep the hilotes down and the fact their economy was rather undevellopped compared to the other city states (they needed the persian gold to survice the Peloponnesian war) and you see that despite its much larger than average territory and its superb land forces, Sparta was not able to create an empire. The way the Spartan logistics were organized (if we believe Xenophon) was also a system that could not go very far because they brought everything with them : once they had to forage, except when in very rich Attica, they were done. The exception of Brasidas raid against the northern Athenian colonies near Macedonia was even more radical, surprising and unexpected because it went against normal Spartan practices of bringing everything and the kitchen sink with them on campaign. But then Brasidas' force was not made of true Spartans...
- Athens was something different. While its political system was restrictive, it was not that unstable, in fact it was even rather resilient as shown by the rather rapid restauration of democracy following the 404 events. It had a very large territory, but also a lot of colonies that created a support network that allowed to support the mainland from the sea in ways no one could imitate. The Delos league only amplified those elements. Athens managed to mobilise 10 000 hoplite forces simultaneously with 11 to 22 000 men naval forces, and to pay for it all thanks to the Delos league's budget and its own considerable ressources. Athens also needed less farmers % in its population thanks to imports from the Crimea that allowed for more soldiers, sailors and industrial workers. Athens had also a very different logistical system based on its coinage : the Athenians mostly did not bring their own food with them, but they rather organized temporary markets and the soldiers bought their food from the locals using the cash they received from their officers. All those elements lead Athens to the level it did, wich many do consider as a kind of empire. But Athens was also constrained by the lack of lands and the geography of Greece, much more complex than that of Italy for instance