How many nuclear warheads (approx.) would be needed to make the Earth uninhabitable to humans?

A limited nuclear war between pakistan and india, with 10 weapons used on each side, would cause particles from the tremendous incineration of wood structures in both countries to be blown into the upper atmosphere...these particles blocking sunlight would cause a "nuclear winter" lasting a few decades with an average of 10C temperature drop in the northern hemisphere... the disruption of agriculture by this cold spell would probably cause mass starvation and subsequent food wars...earth would be marginally habitable, but not civilized... more.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.