1. Political systems: Sparta was a militaristic oligarchy while Athens was a democratic city-state.
2. Economic competition: Athens grew wealthy through trade and sought access to the Black Sea, challenging Spartan control over the Aegean.
3. Warfare: Athenian support of Sparta's enemies and competition over control of regional cities caused tensions.
4. Alliance system: Sparta led the Peloponnesian League, while Athens formed the Delian League. Mutual distrust deepened leading to conflict.
5. Corinthian incident: Corinth (ally of Sparta) clashed with Corcyra (ally of Athens) over Epidamnus, leading Athens to intervene and further strain relations.