If all the nuclear weapons on Earth were detonated, would it be possible to destroy the whole of humanity?

No. Fun nuclear weapons fact. If you detonated ALL the nuclear bombs EVER made (over 80,000 lifetime, about 12,000 left today), the energy released would not even compare…

If the atomic bomb is a 40s technology, why didn’t any other country like Iran or Iraq for example manage to make one in a matter of one day?

Uranium 235 is the magic stuff that makes nuclear weapons possible. It’s not the most common isotope of Uranium though, not by a long-shot. You can order a chunk…