Greece refers to an ancient kingdom ruled by the Ancient Greeks who are native to this region. This civilization consists of many city states such as Athens and Sparta, which were once major cultural and economic centers. They are a playable civilization in Age of Empires and are primarily an offensive civilization.
The Greeks are represented in the first main campaign story-line, which details their expansion from out of the last Ice Age into the city-states and finally under the banner of Alexander the Great.
In the ancient world, Greeks were major trade and colonial powers, setting up colonies in Italy, Cyprus and Asia Minor (now modern-day Turkey. The Greeks fought mostly in large Hoplite armies, and were famous for their hoplites and phalanx formation. The Greeks played a major role in the ancient world, possibly saving Europe from invasions by Persia along with contributing most of the ancient philosophy, mathematics, and other sciences known world-wide today. The Greeks resided in city states that constantly competed for power, especially between the city states of Athens and Sparta. After the Peloponnesian wars, Athens and Sparta (greatly weakened by their conflict) were annexed by Macedon. Greek civilization would reach its peak under Alexander the Great, who conquered most of the known world. His empire, though, was only as strong as he was, and after he died it quickly fragmented and lost power. The Greeks were eventually conquered by the Romans a few centuries BC, and were largely assimilated into their culture.
Greek influence did not die there, however. The Romans borrowed heavily from Greece, including architecture, religious basis, and military tactics. The Eastern Roman (or Byzantine) Empire is commonly referred to as the Greek half of Rome.