High mountains and access to water (the sea, not rivers) meant that
navies were critical for war and trade.
This also meant that the different city states of Ancient Greece were
physically separated from each other.
This allowed each culture to have similarities (like language and
religion), but also significant differences like the Spartan vs. Athens
systems. This also led to a particular
type of farming and a limited ability to fight in open plains. Hence the Hoplite system with phalanxes
became dominant.
