As I’ve pointed out in several of my previous essays, running out of oil will be the most immediate cause for the fall of civilization. It will come sooner than a collapse caused by climate change.
So many critical components of society depend on oil — freight transport (ships, trucks, and airplanes), agriculture (fertilizer and machinery), pharmaceuticals, high-end and specialty plastics (a lot of medical applications), mining (digging and transport), steel, specialty lubricants, cement, and glass — that as oil goes so goes our civilization.