I'll take the liberty to share some notes from unscientific sources, because I find the official sources plain boring. A civilization is generally started by g

I'll take the liberty to share some notes from unscientific sources, because I find the official sources plain boring. A civilization is generally started by great people that put grand ideals into its foundation. A sign of such founders is their borderline unbelievable holiness, that makes them a legend. During its lifespan, great minds get replaced by small minds. The typical lifespan is about a million years, but maybe this time things move a lot quicker. The latter are attracted not to the ideals, but to the earthly things, such as shiny metals and power over others. I believe we are here now. In all cases, such people eventually discover the secret of black magic (I know, many would cough here) and the dark age begins. A sign of that phase is cyclopic brutalistic architecture that worships human body (that's an important detail). We've had a glimpse into that already: nazism. We seem to be moving rapidly in that direction: powerful dictatorships are plenty, while democracies are few. Another sign of that phase is abandoning liberty and reason, because the evil (the dark side of every human) has neither, and embracing chaos and fatalism. Example: the idea that voting doesn't matter, whether it's technically true or not. The terminal stage of every big civilization is a collapse into a sort of a black hole: people are paralyzed by fear and hate, the dominating ideology is a dark cult. There's no coming back from that stage, as that kind of dark cult has real power. At this point, the civilization always gets an external "help" that wipes everything out, so the few survivors could start it over, but now at the next level.