There's no mystery to how prior civilizations hit collapse events when I read comments like this. Every system has a limit, if you don't believe this is the case, you'll likely hit it in catastrophic fashion.
In the year 2018, you'd think people would be more focused on higher pursuits and inquiries about the Universe than just a joy ride from life to death and a maximization driven social trend to see how much money you can make and spend in a lifetime.
Anytime prior civilizations have forgotten about the fundamentals or considered themselves to be so technologically advanced to be beyond the impact of nature, there usually is a reckoning and that reckoning usually occurs at the peak of society when resources are being improperly dedicated to vanity and idiocy. There's a reason the hallmark structures of past civilizations are erected pretty close to their demise.
The Sun goes through cycles we have yet to fully understand.
That alone could cause significant effects to the earth and its something we have zero control over. I'd think it would be a far better social culture to be focused on dedicating resources to exploring and studying the universe and fundamental nature therein than mining clown coins via bit flipping wasting energy/computing resources on a ponzi scheme. However, look how many billions are involved with this.. In a so called modern highly educated society.
As far as population goes, why does a human being feel entitled to have kids? Why are there so many poor individuals having kids? Why should we try to test the limit of nature's carrying capacity? Why do we continue to push the world population higher? We did we create economic models that depend on population growth? Again, a different kind of life from just popping out kids and enjoy the rides of life. A life of inquiry and the pursuit of understanding....
> There's a lot more room left for human growth on this planet
Until there's not or nature throws you a cyclical curve ball. See history for what the results are.