Answer:
The cause will be "Sparta's insecurity and envy about Athens' power as well as resources".
Step-by-step 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.