To me, it is all of the same piece, including over-population.
I suspect that peak oil will strike first, followed by economic downturn and political and military strife, quickly followed by a food production shortfall. As soon as climate change impacts grain production, it is all over. Not to mention, also, that in the USA, aquifer depletion will also strike shortly after all the others have had their bit to play. Our system of organization will basically continue until it cannot any longer and there will then be a complete discontinuity because the two ways of life do not share anything in common and, in the end, climate change will put out any hope for returning to a simpler way of life. I don't think one can get any more doomerish than that scenario. All coming within 100 years and, possibly, much less, but that is the only unknown to me.