Answer:
The most important and crucial reason why Peloponnese war was because Sparta was jealous of the increasing wealth Athens was acquiring. It rebuilt itself to conquer its allies. To become better and stronger.
Step-by-step explanation:
Sparta was jealous because Athens was acquiring wealth and it did not set well with Sparta.
Upon receiving the wealth and seeing an increase in it, the Athens started bullying its allies as well. They wanted to become the best. They wanted to defeat everyone when it comes to war.