>>5
Peak oil is certainly part of it. However, Humanity has painted itself into a corner of sorts. It's not just oil. A lot of the easily-obtained resources have been partially to wholly depleted. No, we'll never actually "run out of oil" ... it's just that each additional barrel of oil must cost more to extract than the last. Over the next decades of the 21st Century, that truth will become more and more apparent until even the most doltish of deniers (like Rush Limbaugh) will have to admit that you don't need to actually run out of oil in order to practically run out of oil
Like I said, it's not must oil. The cheap extractions of strategic metals like copper, gold and chromium have already been done. What remains is larger or more involved operations to filter out those metals from poorer ores. That will just drive up the costs. Eventually, we won't be able to afford to use platinum in our catalytic converters. What happens then? well, our civilization as we know it will degrade by yet another notch point.
We have the ability NOW to drive technological expansion such that we actually do expand general Human civilization into space. However, that can't be done while people would rather put investment capital into useless enterprises, like stock and bonds. In order to achieve space, we have to do all that unsexy manufacturing stuff, and at a low (primarily, losing) margin. The end product will take a lot longer to pay off ... and when it does, by hauling a trillion-ton asteroid into Earth orbit, it will do so handsomely. But what Western investor will make a 30-year investment at such high risk, no matter how many trillions such an asteroid is worth even on a glutted metals market?
Hence:
THE WEST HAS FORGOTTEN HOW TO EXPAND A CIVILIZATION. And so, it will fall, and the bailiwick will be passed to another civilization. However, the disease of financial greed has infected much of Humanity. If a civilization like China manages to inherit the world, they will have a tiny window of opportunity in which to expand Humanity outward beyond the atmosphere. In my opinion, that window is just too small. Some might argue that that window doesn't actually exist since a nation of China has started off on the wrong foot from the beginning, since it expects to engage in investment frauds immediately.