To understand Greek History and lot of what we associate with "Greece" and what we saw on our trip, one has to understand the geography. In this case, Geography was very determinative in how we understand "Greece".
As a historical country, Greece (Ἑλλάς pronounced "Hellas", thus the ancient reference to the Hellenes) is a part of the Balkan Peninsula of the main European continent consisting not only of the attached land mass itself, but also of the islands of the Agean, Ionian, and Mediterranean (over 6,000 in the current Greek republic):
Another unusual feature of Greece is the fact that mainland narrows at one point to 3.9 miles/6.3 km. Known as the Corinthian Isthmus which is bounded by the Gulf of Corinth and the Saronic Gulf, this effectively separated the mainland of Greece (Attica and Boeotia) from the Peloponnesian Peninsula, thus creating a sharp divide between the two geographies (and making Corinth fabulously wealthy as a transfer point in the process).
The geography of Greece is largely mountainous (80%) with limited plains (making it, at least in that way, like Japan) with one of the most extensive coastlines in the world (11th longest); one is never too far removed from either the mountains or the sea.
All of this, of course, has impact.
To the Greeks, the sea was never seen as a barrier but rather as a highway: the first Greek civilizations of the Cyclades and Minoans were actually based on islands and the Mycenean culture used the sea for trade and invasion, as the Trojan War alludes to (and modern archaeology suggests). The sea also allowed the Greeks to colonize and expand throughout the larger Mediterranean and beyond. The Greeks became great travelers, merchants, and colonists.