After the collapse of the Achaean kingdoms around 1200 B.C., the Greek cities fell into decline and the country entered into a dark age so profound that even the skill of writing was evidently lost for several hundred years and the classical Greek alphabet reflected nothing of the Mycenaean syllabary. After several centuries it emerged as the center of a brilliant new civilization, though, to which we owe hugely significant developments in philosophy, mathematics, history, politics and theater, among others.
The basic unit of Greek civilization was the polis, or city-state, a small country centered on a market and acropolis with a citizenship who usually felt a sense of ethnic kinship in a remote, mythological past. Hundreds of these filled Greece, and others called apoikia (colonies) were founded around the Mediterranean, especially in southern Italy and Asia Minor, but also in North Africa, Italy, and Sicily. Usually a polis was ruled by an oligarchy, but the oligarchy never had the divine power of contemporary eastern rulers, in part because the commoners played a larger role in the economy and defense (as hoplites) of the state. Towards the seventh century a number of tyrannies were also established, meaning they were ruled by a tyrant, a usurper supported by popular opinion against the oligarchy (see Pisistratus).
In the seventh and sixth centuries many cities came to be ruled as democracies. A variety of systems of voting and govenment shared the general name, which was felt in Greece to reflect the rule by the demos or people. The democracy known in most detail is the Athenian democracy.
Hellenic civilization reached the peak of its power duing the 5th Century BC. In 478 B.C., following the defeat of the Persian invasion, Athens assumed leadership of an alliance known as the Delian League, which would later come to be known as the Athenian Empire. Sparta, the other great power in Greece, and leader of the Peloponnesian League, fearing the growth of Athenian power, sparred with Athens throught the middle of the centurey. Finally, the two sides fought in the Peloponnesian War, from 431-404 B.C., which involved virtually every state in Greece, including colonies in Asia, Italy, and Sicily. The war ended in the decisive defeat of the Athenian Empire, and severely weakened Greek power, paving the way for the conquest of Greece.
The usual periodization practiced by modern historians is to see the death of Alexander the Great in 323 B.C. as dividing the Hellenic period from the Hellenistic. The shift from "Hellenic" to "Hellenistic" represents the shift from a culture dominated by ethnic Greeks, however scattered geographically, to a culture dominated by Greek-speakers of whatever ethnicity, and from the political dominance of the city-state to that of larger monarchies.