No. The recent FEMA guide on response to nuclear weapons gives a good idea of the consequences. If all nukes that Russia and the US have were detonated on cit

No. The recent FEMA guide on response to nuclear weapons gives a good idea of the consequences. If all nukes that Russia and the US have were detonated on cities then there would still be quite a bit of habitable land in both. There would be a global famine and economic contraction that would lead to untold suffering and wars. Society would slip backwards for the first time in hundreds of years. It is really quite unlikely that it would be the end of history.