Even the losers - we borrow many ideas from plenty of failed civilizations.

And many ideas are also simply lost, history is full of the ebb and flow of advancement as civilizations are destroyed and plundered.

Despite these catastrophic civilization collapses, civilizations have grown increasingly more advanced despite a localized minimum.

The need to wage war to defend or gain resources seems like a major driver of complexity. To maintain a military it needs equipped and fed, requiring large supply chains, and hence, more complexity. If you didn't need to defend your food stores, you wouldn't need such complexity.