I have a friend who is convinced that we're already mid-collapse and have been for decades. He cites many of the same causes found in the link above. He says, "just look at what happens to any wild animal when there aren't enough resources or they're stressed, they start going crazy: self harm, eating young, death by refusing to eat."

He sees echos of behavior patterns like a fractal, so tiny patterns of behaviors in mice emerge as patterns in larger human society. He has said that he thinks human societies are just another organism that lives, ages, and dies. He doesn't really prep or anything, just expects he and most people he knows to die in food riots sometime in his life. He doesn't even bother prepping (so he says) because such a collapse likely would come from a way that he can't expect and wouldn't likely survive anyway. He realizes there isn't enough ammo to hold off millions of starving people, and the people who survive likely would do so accidentally or through freak luck, but a new society would emerge again in a few generations to repeat the cycle again. Fun guy, my friend.