The fundamental cause of the peloponesian war was

The cause will be "Sparta's insecurity and envy about Athens' power as well as resources".

Explanation:

Sparta's fear of Athens rising in influence was the key explanation for both the beginning of that same Peloponnesian. Athens as well as Sparta had waged the Peloponnesian War. They were always very important or strong Greek city-states but instead continued to fight together throughout the Persian invasion.

So that the above would be the correct answer.

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