What cause a major difficulty in uniting ancient Greeks?

A major difficulty in uniting ancient Greeks was their strong sense of local identity and allegiance to individual city-states, or poleis, such as Athens, Sparta, and Corinth. Each city-state had its own government, laws, and customs, fostering a competitive rather than cooperative spirit. Additionally, geographical barriers like mountains and the sea contributed to isolation and hindered communication, making it challenging to forge a unified Greek identity. These factors, combined with ongoing rivalries and conflicts, made large-scale political unity difficult to achieve.