Excerpts from Books and Wikipedia
"While the Greek cities on the coast were sending out boatloads of colonists to the east and to the west, the Spartans armed themselves, crossed over the Taygetus mountain range on their western border, and attacked the city of Messene, which lay on the other side. . . . It was not an easy conquest; Tyrtaeus says that the Spartans and Messenians fought for twenty years. But by 630, Messene had become a subject city of Sparta. Sparta was no longer simply a Greek city: it was a little kingdom. In this Spartan kingdom, the conquered Messenians became a whole class of slaves, who grew food for their captors on terms as harsh as anything found in medieval feudalism: “Just like asses, worn out by their mighty burdens,” Tyrtaeus says, “they bring to their masters through wretched necessity a half of all the fruit that the land brings forth.” The Spartans themselves became the aristocracy, a master race of warrior men and mothers of soldiers. . . . But the real power in Sparta was neither king, nor priest, nor even the Council of Twenty-Eight. The Spartan state was ruled by a strict and unwritten code of laws that governed every aspect of Spartan existence."