How can one explain the fact that the Greeks, having successfully repelled the invasion

How can one explain the fact that the Greeks, having successfully repelled the invasion of the Persians, were defeated by the king of Macedonia?

This can be explained by the fact that the Greeks united to fight the Persians, and when they were threatened by Macedonia, this did not happen. That is, the Greek city-states continued to compete with each other. Naturally, this was in the hands of Macedonia and, thus, she was able to defeat the Greek army. The decisive battle took place in 338 BC at the Battle of Chaeronea. Here Athens was defeated, after which a significant part of Greece was captured by Macedonian troops.