What primary factor encouraged Greek city-states to develop different identities?

The primary factor that encouraged Greek city-states to develop different identities was their geographic isolation due to the mountainous terrain and numerous islands. This physical separation fostered distinct political systems, cultures, and customs as each city-state (polis) adapted to its unique environment and resources. Additionally, competition for trade and resources further emphasized their individual identities, leading to diverse forms of governance and societal norms.