Mad Max's worldMAD MAX'S WORLD
Some Damned Thing in the Middle East led to a limited US-Soviet atomic war in the early 90s. Although neither country got more "than it's hair mussed" (in the immortal words of Dr. Strangelove) it brought about a global economic collapse, while the final nuclear "spoiler" attack against the Mideast oil fields brought about a huge oil price spike: the massive costs of rebuilding and decontamination meant that the world had essentially reached "peak oil", in the sense of decreasing returns on investment, by 2000 AD.
These problems were compounded by global warming-induced climate change, and the "memetic plague" of the Nihilist cult, which preached a philosophy of dealing with a violent and meaningless world too corrupt to be saved by punching it in the head first. The global economy remained stuck in low gear throughout the 1990s and 2000s. A series of bloody wars fought over resources, water, etc. broke out by the mid-2010s, while the US began slowly to descend into civ