Athens thrived because
1. There were glorious and meager times for both.
2. The political power of Athens rose to its peak after the Persian Wars when the Athenians founded the Delian League. It was then, that Athens became the leading power in the Greek world. After the defeat in the Peloponnesian War that followed some decades later, the Athenians never gained this role again (although-always arrogant-they never admitted it).
3. On the other hand, the Spartans, a leading political power in Peloponnese from the archaic period, became the absolute power after the Peloponnesian War…for a while. Exhausted and corrupted, they, too, were soon left behind, as the Thebans initially and the Macedonians afterward took the lead.