Estimates of the loss of life in just Russia and China in the first 6 months after a nuclear exchange: 380 million. Source: RAND (http://www.nybooks.com/articles/2018/01/18/daniel-ellsberg-n...).

"Moscow alone was targeted with at least eighty nuclear weapons, and every Russian city with a population greater than 25,000 would be hit by at least one."

And that was the December 1960 plan.

There was a great article which I can't find now about all the missiles still pointing from the US to Russia and vice versa, where after the fall of the Soviet Union a General formerly in charge of the Soviet arsenal met his British counterpart and assured him that in the Soviet nuclear war preparedness plans, the entire UK was a complete overkill zone.

Why two centuries? Most areas of the world are extremely unlikely to be involved in a nuclear conflict and/or receive significant damage.

Two centuries is somewhat arbitrary, because there are so many assumptions in the notion of "large scale nuclear conflict" as is. Areas that aren't direct targets of nuclear weaponry will still suffer major setbacks, as supply chains for various goods and resources are disrupted. Present day problems, like hunger, access to medical care, and safe drinking water would just become magnified. For example, a nuclear conflict could potentially cascade into a much more dangerous famine, because supply for modern pesticides and agro-chemicals is temporarily destroyed. Supply chains for antibiotics could be disrupted, resulting in outbreaks of various preventable illnesses. If you total all the possibilities up, I suspect the secondary impacts of nuclear conflict would be worse than the actual warfare.

If oil production is destroyed, I assume the secondary impacts will be catastrophic.

Two centuries ago some of us would have been slaves. I’m not entirely sure I would want to live through that setback.