mutants
The main one has been the terror of the cold war and all the side effects from that terror.
This is actually a rather complicated situation.On the "yes" side: Japan certainly has the expertise, technology and equipment to construct nuclear weapons. They also have ready access to weapons-grade raw materials.On the "no" side: Japan has a non-nuclear policy (to be clear here: that refers to weapons, not reactors for generating power) and construction of nuclear weapons may be forbidden by their constitution (whether or not small "tactical" nuclear weapons would be forbidden is a question of interpretation). So far as is known, they've never conducted any nuclear weapons testing... and the US would almost certainly know if they had.Probably the best answer is: there's no particular reason to believe that Japan has nuclear weapons at this moment, but there's also no particular reason to believe they couldn't put one or more together on very short notice if they really wanted to.
death
Because there was no true defense against nuclear weapons. Once both sides had nuclear weapons, the only way to "protect" themselves from the other side was to have so many more nuclear weapons that even if their enemies used all of their nuclear weapons, there would still be nuclear weapons to shoot back with. That way, nobody would use nuclear weapons, because they could never actually "win" that way. This thought process was referred to as Mutually Assured Destruction, or MAD.
Nuclear weapons do not deter terrorists and indeed the use of nuclear weapons appeals to terrorists. During the Cold War large superpowers acheived a stalemate since neither side wanted to start a nuclear conflict which could result in Mutual Assured destruction however terrorists have no such concerns.
Probably.
There are many side-effects to testing in animals such as permanent brain damage, cancer, and even death.
to ensure each side remained vulnerable to the others nuclear weapons.
All animals get side effects. Most die or are left severely maimed, and those who do not die are kept in cramped, unsanitary conditions until they do.
The Soviet Union was working on nuclear weapons and a weapons race begun. They were terrified of each other.
It is a dangerous technology that could wipe out the majority of the world's population in a couple of hours. Besides, Mexico does not have any enemies, thus by banning nuclear weapons on its soil, Mexico has a moral advantage in case it is attacked by a nuclear power (i.e. it would be considered an atrocity, forcing many nations to side up towards Mexico in case of a nuclear attack).
I believe it would very likely become a hot war long ago, probably a conventional WW3. Nuclear weapons scared people a lot, but probably prevented another global war.