I like the way you think. Imagine if today the oil trade stopped completely. In a matter of months, the civilization as we know it would collapse. Even with th

I like the way you think. Imagine if today the oil trade stopped completely. In a matter of months, the civilization as we know it would collapse. Even with this current crisis, we are seeing a sharp decline in the standard of living. Well the grain was as important or even more important to the ancient societies than oil is to us. Without it, the civilization would revert to tribal hunting and gathering of food. We can argue about the role of religion for the lack of prosperity but without cultural and spiritual connection provided by organized religion, people would not band together as they were. Grain alone was not enough. Only when science allowed for more comfort and easier transportation (railroads, ships, roads, sturdy homes, etc.), did people start putting religion aside. I would argue that some ancient civilizations were more advanced when compared to some medieval nations. Trade disruption was not the only reason why those civilizations fell. The lack of a reliable way to preserve knowledge was another. Now, imagine what would happen if modern humans lost access to Internet for a couple of years. It was about several orders of magnitude worse when ancients lost written knowledge that was kept, most of the time, in a well renowned place. One such example was the Library of Alexandria. Imagine all the secrets and ancient technologies that were lost when they burned it.