Greek History > Geography
Most of Greece contains either islands or mountains which lent to the decentralized nature of their civilization. This is why it was hard for Greece to unify as a single political entity and ended up becoming independent and autonomous city-states with a common culture. Being located right on the Mediterranean and because of the islands maritime trade flourished and the Greeks were in contact with many other cultures throughout the ancient world.
There was also a lack of fresh water in Greece which also inhibited their agricultural capacity or ability to sustain large urban populations. The climate however, in Greece had warm, wet winters and hot, dry summers which was perfect for the cultivation of olives whose oil became a major trading good throughout the region. Other options like animal domestication existed for the Greeks as well.
See Greek Economy
The Greeks were dependent on trade for materials not available in their rocky and island region. While they had lots of rock and marble for the construction of later temples, the Greeks lacked much agricultural land or metals and thus had to trade for them with civilizations around the Mediterranean and Near East.