When our farmer ancestors warred, they often went about as far as they could to apply all available resources to their war efforts. This included converting plowshares into swords, ships into navies, farmers into soldiers, granaries into soldiers on the move, good will into allies, and cash into foreign purchases. When wars went long and badly, such resources were often quite depleted by the end. Yet warring farmers only rarely went extinct. Why?
The distinction between stock and flow is a basic one in engineering and finance. Stocks allow flows. A granary is a stock, and it can produce a flow of grain to eat, but that flow will end if the stock is not sufficiently replenished with every harvest. A person is a stock, which can produce work every week, but to make that last we need to create and train new people. Many kinds of stocks have limits on the flows they can produce. While you might be able to pull grain from a granary as fast as you like, you can only pull one hour of work from a worker per hour.
Natural limits on the flows that our stocks can produce have in the past limited the destructiveness of war. Even when war burned the crops, knocked down stone buildings, and killed most of the people, farmland usually bounced back in a few years, and human and animal populations could grow back in a few generations. Stones were restacked to make new buildings. The key long-term stocks of tech and culture were preserved, allowing for a quick rebuilding of previous professions, towns, and trade routes.
Future technologies are likely to have weaker limits on the conversion of stocks into flows. When we have more fishing boats we can more quickly deplete the stock of fish. Instead of water wheels that must wait for water to come down a stream, we make dams that give us water when we want. When we tap oil wells instead of killing whales for oil, the rate at which we can extract oil grows with the size and number of our wells. Eventually we may tap the sun itself not just by basking in its sunlight, but by uplifting its material and running more intense fusion reactors.
Our stronger abilities to turn stocks into flows can be great in peacetime, but they are problematic in wartime. Yes, the side with stronger abilities gains an advantage in war, but after a fierce war the stocks will be lower. Thus improving technology is making war more destructive, not just by blowing up more with each bomb, but by allowing more resources to be tapped more quickly to support war efforts.
This is another way of saying what I was trying to say in my last post: improving tech can make war more destructive, increasing the risk of extinction via war. When local nature was a key stock, diminishing returns in extracting resources from nature limited how much we could destroy during total war. In contrast, when resources can be extracted as fast and easy as grain from a granary, war is more likely to take nearly all of the resources.
Future civilization should make resources more accessible, not just to extract more kinds of slow flows, but also to extract fast flows more cheaply. While this will make it easier to flexibly use such stocks in peacetime, it also suggests a faster depletion of stocks during total war. Only the stocks that cannot be depleted, like technology and culture, may remain. And once the sun is available as a rapidly depletable resource, it may not take many total wars to deplete it.
This seems to me our most likely future great filter, and thus extinction risk. War becomes increasingly destructive, erasing stocks that are not fully replenished between wars, and often taking us to the edge of a small fragile population that could be further reduced by other disasters. And if the dominant minds and cultures speed up substantially, as I expect, that might speed up the cycle of war, allowing less time to recover between total wars.