Why Did Megara Become a Focus of Greek Conflicts After

Why did Megara become a focus of Greek conflicts after the Persian Wars? ?

A) Both Athens and Corinth wanted to control Megara's trade.
B) It was the wealthiest polis in Greece.
C) Megara's democratic government was a threat to Sparta.
D) It was a heavily fortified refuge against Persian attack.
E) Corinth feared that Megara would ally with Sparta.