Great question. Arguably the greatest factor in shaping a people is the geography and location of land. When we talk of the ancient Greeks, we need to remember three very important points about their geography and location.
First, Greece is very mountainous. About 70% of Greece is divided by mountains. This means that cities sprouted up that were separated from each other. In this way, the history of Greece is not the story of an empire but individual cities. Just think of these individual cities, such as Athens, Sparta, Thebes and Syracuse.
Second, Greece was always close to the sea. In fact, almost 90% of all Greek cities were 25 miles from the shore. Hence, the Mediterranean sea was not so much a hinderance but a highway for travel. This is an important point to keep in mind.
Third, Greece lacked natural resources. So, they were forced to trade and travel. Hence, the Greeks became great seafarers. This enabled them to colonize around the Mediterranean and interact with other cultures.
In time, the Greeks would spread. This enabled hellenism to be a powerful force.