The Greek 'Dark Age' drew to a close as a significant rise in population allowed urbanized culture to be restored, and the rise of the city-states (Poleis). These developments usher in the Archaic period (800-480 BC). They also restored the capability of organized warfare between these Poleis (as opposed to small-scale raids to acquire livestock and grain, for example). The fractious nature of Ancient Greek society seems to have made continuous conflict on this larger scale inevitable.
Concomitant with the rise of the city-state was the evolution of a new way of warfare - the hoplite phalanx. When exactly the phalanx developed is uncertain, but it is thought to have been developed by the Spartans. The chigi vase, dated to around 650 BC, is the earliest depiction of a hoplite in full battle array. The hoplite was a well-armed and armored citizen-soldier primarily drawn from the middle classes. Fighting in the tight phalanx formation maximised the effectiveness of his armor, large shield and long spear, presenting a wall of armor and spearpoints to the enemy.
With this evolution in warfare battles seem to have consisted mostly of the clash of hoplite phalanxes from the city-states in conflict. Since the soldiers were citizens with other occupations, warfare was limited in distance, season and scale. Neither side could afford heavy casualties or sustained campaigns, so conflicts seem to have been resolved by a single set-piece battle.
The scale and scope of warfare in Ancient Greece changed dramatically as a result of the Greco-Persian Wars. To fight the enormous armies of the Achaemenid Empire was effectively beyond the capabilities of a single city-state. The eventual triumph of the Greeks was achieved by alliances of many city-states (the exact composition changing over time), allowing the pooling of resources and division of labour. Although alliances between city states occurred before this time, nothing on this scale had been seen before. The rise of Athens and Sparta as pre-eminent powers during this conflict led directly to the Peloponnesian War, which saw further development of the nature of warfare, strategy and tactics. Fought between leagues of cities dominated by Athens and Sparta, the increased manpower and financial resources increased the scale, and allowed the diversification of warfare. Set-piece battles during the Peloponnesian war proved indecisive and instead there was increased reliance on attritionary strategies, naval battle and blockades and sieges. These changes greatly increased the number of casualties and the disruption of Greek society.
Following the eventual defeat of the Athenians in 404 BC, and the disbandment of the Athenian-dominated Delian League, Ancient Greece fell under the hegemony of Sparta. However, it was soon apparent that the hegemony was unstable, and the Persian Empire sponsored a rebellion by the combined powers of Athens, Thebes, Corinth and Argos, resulting in the Corinthian War (395-387 BC). After largely inconclusive campaigning, the war was decided when the Persians switched to supporting the Spartans, in return for the cities of Ionia and Spartan non-interference in Asia Minor. This brought the rebels to terms, and restored the Spartan hegemony on a more stable footing. The Spartan hegemony would last another 16 years, until, at the Battle of Leuctra (371) the Spartans were decisively defeated by the Theban general Epaminondas.