> A future nuclear war would not only reduce cities and towns to ruins. Fallout from the nuclear explosions would spread through the atmosphere, bombarding the land with lethal amounts of radiation. The only means of escape would be to live in deep underground shelters away from the fallout. This imprisonment would have to last until the radiation decreased to an acceptable level, which could take many years. Even then, climatic changes, shortage of food and the threat of disease would make life above ground a grim business.
Incidentally, the book is most memorable for lucid and well-explained diagrams involving woolly mammoths, and I highly recommend it for explanations of anything mechanical. The section on nuclear physics is a bit lackluster, however.