Final answer:
The Peloponnesian War began due to a mix of Athenian imperial ambitions post-Persian War and growing fear and resentment from Sparta and its allies. Athenian efforts to influence Spartan allies and Athenian aggression prompted Corinth to seek Sparta's intervention, leading to war in 431 BCE. Cultural shifts and a transformation of Greek society followed the war's conclusion.
Step-by-step explanation:
The attitudes that led to the start of the Peloponnesian War included a mix of fear, resentment, and burgeoning pride among the ancient Greek city-states, notably Athens and Sparta. After their victory in the Persian War, the Greeks developed significant confidence in their civilization. This newfound pride, however, soon devolved into imperial ambitions especially on Athens's part, leading to Athenian aggression. Athens's expansionist policies, which resulted in the Delian League, were viewed as a threat by Sparta, the head of the Peloponnesian League. Sparta and its allies felt intimidated by Athens's growing power and were resentful of its influence over other Greek poleis. This tension escalated when Athens attempted to influence the political decisions of Spartan allies.
Furthermore, the cultural and intellectual competition between the city-states contributed to a sense of rivalry. Both Athens and Sparta's alliances sought to assert their dominance within the Greek world. The eventual clash came about when Corinth, a member of the Peloponnesian League, requested Sparta's intervention against Athenian aggression, culminating in the invasion of Attica by Sparta and its allies in 431 BCE. This war not only highlighted the political and military conflict but also represented a collision of ideologies and social systems between oligarchic Sparta and democratic Athens.
By the war's end, the war's ravages had transformed Greek society, undermining the hoplite-based social order and forging new cultural and political landscapes. In Sparta, the war's necessities such as diplomacy and naval power reformed its identity, lessening cultural xenophobia and requiring a shift towards skill and education over pure military might. Overall, the Peloponnesian War checked Athens' imperial ambitions and forced Greeks to reconsider their perspectives on their non-Greek neighbours, resulting in cultural as well as political shifts.