"The energy resource that we learned to develop this time is fossil fuels, starting with coal about 1800. World population was able to expand greatly because of additional food production permitted by fossil fuels and because of improvements in hygiene. A period of stagflation began in the 1970s, when we first encountered problems with US oil production and spiking oil prices. Now, the question is whether we are approaching the Crisis Stage as described by Turchin and Nefedov."