WHEN Helen, the wife of Agamemnon's brother, Mene-laus, was abducted by Paris, a Prince of Troy (or Ilium), the wealthy city at the southern entrance of the Dardanelles, Agamemnon led an expedition against Troy. The city fell after a siege of ten years. Such is the account given in the Iliad of the poet Homer. It has been suggested that the real cause of the war was the founding of Greek settlements in Aeolis, on the north-west coast of Asia Minor, which Troy attempted to oppose. The war, as Homer's other immortal poem, the Odyssey, reveals, caused widespread unsettlement in Greece, with the result that, about a century later, the land succumbed to the invading Dorians. Although a branch of the same race as the Achaeans, the Dorians did not mix with them, but either expelled them completely or enslaved them. Attica alone escaped invasion, for its poor soil offered no attraction to the conquerors. The strongest Dorian state was that of the Spartans in the Southern Peloponnese, who, although far outnumbered by them, enslaved and oppressed the natives, called Helots. The wave of invasion extended to Crete and to Doris, the south-western coast of Asia Minor. The expelled Greeks colonised lonia, the central division of the western coast of Asia Minor. This district, with Aeolis and Doris, formed a fringe of Greek settlements from the Dardanelles to Rhodes. These towns, taken over from native settlers, and situated at the terminal points of caravan routes from the East, prospered exceedingly. They first felt the fertilising influences of the older civilisations and showed their Motherland the way to scientific and intellectual progress. Greek history is obscure after the Dorian conquest, until, in the seventh century B.C., we find the land divided among various city-states. There was Athens, which included the whole of Attica ; Sparta, ruling most of the South and West Peloponnese : Argos, strong in the North-East Peloponnese; and Boeotia, a confederation north of Attica, under the leadership of the city of Thebes. The struggle for mastery between these states lasted till they all fell to Philip of Macedon in 338 B.C.