Assume that the world's superpowers engage in a full out war with today's existing arsenals of nuclear weapons. Civilization destroyed, billions dead, and all that.
Fifty years later, what does the world look like? In countries not directly involved in the war, will fallout and secondary contamination be significant enough to cause mass illness and/or death? In countries directly targeted (such as the USA), is it plausible that anyone could survive the initial war and immediate aftermath, and rebuild any semblance of civilization? How dangerous and widespread will surface radioactivity be after that time, and will water sources be safe to drink? Will it be safe and possible to farm or fish downwind of areas targeted by nuclear devices? Is it likely that the governments of countries involved in a nuclear exchange would survive in any meaningful fashion?
I recall it being said that air-burst nuclear explosions don't create much long-lasting fallout, but in a full nuclear exchange there would be quite a few ground bursts, right? How long will those areas remain dangerous?