The fragmentation of the Greek city-states is best explained by their

While Spartan aggression played a role in the conflict, it was largely a reaction to Athenian imperialism. Sparta's military responses were motivated by the need to counteract Athenian expansion rather than being the primary instigator of the war. Thus, Spartan actions were responses to Athenian policies rather than the root cause.

Athenian imperialism drove the rise of conflict as Athens sought to expand its influence over the Delian League and impose its will on other city-states. This expansionist policy alarmed Sparta and its allies, creating a fear of Athenian dominance that ultimately led to the war. The imperialist ambitions of Athens directly contributed to the hostilities that ignited the Peloponnesian War.

Athenian democracy itself was not a direct cause of the Peloponnesian War. Although the democratic system allowed for aggressive policies and expansion, the conflict arose primarily from the imperialistic pursuits of Athens rather than the nature of its government. Democracy facilitated decisions but was not the core issue leading to the war.