A few hundred or thousand nuclear bombs dont kill all humans and dont destroy this planet, there will be billions of people who will survive a new world war.
Nearly all people in africa, south america asia and so on will survive imo.
How can you be sure that no nukes will be dropped in Africa, Asia.etc? If a world war actually happens, then most of the world nations (including those from South America and Africa) are likely to side with one of the two warring factions. And also, today's nuclear weapons are 100x to 1,000x more powerful than those bombs which were dropped in Hiroshima and Nagasaki. Even if they are dropped in Europe, the effects will reach Africa and Asia.