First things first, what came before the Classical Greeks? The collapse of a thriving Mediterranean into a "dark age" of international chaos.

Truly, the Bronze Age was magnificent. Large kingdoms and empires extended over post-migratory peoples beginning to farm in the mild climates of the Mediterranean. Law was created soon after the written word, and these underpinned the economic bounty which is a feature of all most successful human periods. Borders and domains are not as concrete as in later times. Egypt comes to own much of the Levant and vies with Hittites on a big scale. Small tribes and city-states also fight for control over smaller tracts. Both are after arable land, resources and cities on trade routes.

Many theories abound as to why the Bronze Age society collapsed, ably explored in the book 1177 B.C.: The Year Civilization Collapsed. This is the period where you hear about the "Sea Peoples." I have found that Cline's book specifically but neglectfully addresses the possibility of famine and population decline due to soil degradation. The link is to the pertinent 6 minutes of a talk by the author of Dirt: Erosion of Civilizations, in which he discusses the mechanics, apparent effects, and reaction to this possible cause.

The next chapter, so to say, is the Greek "dark age" of which I know less about. I hope someone will come along to fill us in on Dorians and the formation of poleis.

They weren't stifled by Christianity. Lived in a magnificent landscape and climate.