The ebbs and flows of society within history are longer than a few years or even a single generation. The general trend for civilization in recorded history is up. But within that trend there are peaks and valleys that may span up to several generations. There are periods of peace and stability that have lasted for hundreds of years (like the Pax Romana). Then there are entire centuries plagued by wars, famine, and plague.
We have lived in relative stability since WW2. Perhaps that will go on. Perhaps that will not. But it's been less than 70 years since WW2. The period of stability and prosperity that we've experienced since then is still short compared to similar periods in history, but it's long enough for us to forget many of the lessons we've learned.
A fundamental mistake every generation makes in youth is to say "we are different", "we are special". Maybe we are. But history shows that when something rocks the boat, "civilization" can degenerate very quickly into base survival instincts, which are not pretty.
Humanity is perpetually marching towards something better, but I think it's a mistake to take comfort too deeply in the facades of comfort and stability we build for ourselves. Fundamentally, we are still animals, and it takes less than most people imagine for that part of our lineage to reassert itself.