What was one reason that Macedon was able to conquer the other Greek
City States?

C. The Peloponnesian War had weakened the Greek City States.

Explanation:

The one reason that Macedon was able to conquer the other Greek

City States is the Peloponnesian War had weakened the Greek City States.

The Peloponnesian War refers to the war that took place between Anthens and Sparta, two most powerful city-states in ancient Greece. The war brought a significant shift in power in ancient Greece and it favored Sparta.  It then led to regional decline.

When Argead king Philip II (359–336 BC) reigned, Macedonia subdued mainland Greece and also subdued the Thracian Odrysian kingdom. As a result of the Peloponnesian War, the Greeks were weakened from fighting which enabled Phillip of Macedonia able to easily conquer them.