TSW: Wagner: "peoples never merely capitulate to environments. Indomitably, they work to change (them)."
BW: In this case, an obscure sociologist got it right. Humans, like other animals, aren't "victims" of their environment, but actively change their environments to serve their own needs. Saying that people are part of the "univironment" is an evasion. Obviously, they change the "external" circumstances to suit their "internal" needs, rather than just adapt to what exists. Many other animals do that instinctively and are therefore less subject to being "selected out" by the natural environment.
BW: Somewhat relevant, but mostly incidental, if you view "civilizations" as the degree of civility in a society. If population density were the primary criteria, then Mumbai, India is the most civilized major city in the world and Denver, Colorado is the least civilized:
TSW: "No civilization has fallen without a decline in population."
BW: Armed invasions of civilized countries tend to reduce populations, but mainly in the military. Empires tend to lose territory on their periphery, which reduces population within the empire, even if very few people die. The primary reason the Roman Empire lost population was because of the Antonine Plague, but it actually increased population prior to the Empire's downfall:
BW: The population of England grew by a million every decade, throughout the U.S. colonization and development:
... as did France:
Beyond population, there's no indication that there was any decline in "civilization" in any of the "Mother Countries", with the possible exception of the deaths during the Irish Famine.
So, your proposition is evidently false.
Next: The Social Microcosm (Part 6 of 7)