Cultures may have been able to carve out niches—or kingdoms, or even empires—for themselves along the Missouri or Seine or Yangtze or Ganges or Kwanza—but none of them would have enough insulation from the neighbors to persevere. Other groups—whether civilized or barbarous—would wear these echo cultures down with unrelenting competition. Even the biggest and most badass of all those echo empires—the Romans—“Only” survived for five centuries in the dog-eat-dog world of early history. In contrast, Mesopotamia and Egypt both lasted multiple millennia.
