Theories of geographical determinism go back at least to the 5th century BC. Herodotus famously claimed that hard country breeds hard men, while gentle lands with moderate climates make for weaker people. He used this to explain why the Persians had risen to power, and why the Ionians of the coast of Asia Minor were constantly being ruled by one great power or another. The idea was that hard land makes men work hard to survive, and makes them indifferent to hardship and want, whereas those from rich and fertile areas wallow in their luxury and become lazy and complacent.

In practice, of course, this is a very doubtful premise. For one thing, the Persians were the first non-Mesopotamian people to rule Mesopotamia; most of its great empires (Assyria, Babylon, Akkad) were home-grown in the fertile floodplains of the Two Rivers. For another, while neither Attica nor Laconia (the hinterland of Athens and Sparta respectively) could count as an agricultural paradise, they were still some of the richest lands in Greece. Athens was further helped by the fact that Attica contained a very rich silver mine. Meanwhile, truly mountainous and inhospitable areas like Arcadia remained backwaters for most of Greek history.

Something similar may be said of Rome. It may not have been built on a flatland, but it wasn't exactly an arid highland like Bruttium or Samnium - the sort of territory that Rome would eventually come to dominate.

There is a question here to what extent a Mediterranean state could be anything but hilly or mountainous. The geography of the entire region is rather rugged. Given that context, places like Sparta, Athens and Rome were actually relatively low-lying, flat and fertile. Many other regions were less hospitable, and few of those rose to great prominence.