What was the primary cause of the Peloponnesian War?

The primary cause of the Peloponnesian War was the rivalry between Athens and Sparta. This conflict arose from longstanding tensions between the two powerful city-states, which represented different forms of governance and social structures. Athens was known for its democratic ideals and naval power, while Sparta was characterized by its militaristic society and oligarchic government.

As Athens expanded its empire and influence, particularly during its leadership of the Delian League, it created fear and hostility in Sparta and its allies. The competition for power and resources, along with differing political and military strategies, ultimately led to open hostilities in the form of the Peloponnesian War. This war was not merely a local struggle; it had profound implications for the entire Greek world and showcased the tensions inherent in Greek city-state politics, which could be traced back to their contrasting values and ways of life.