During the Cold War American and Russia were engaged in an arms race -- America couldn't allow anyone to be stronger than we were, because it was a distinct possibility that if that happened they would go ahead and attack. But unfortunately the Russians felt the same way; as both nations were quite rich and powerful, it seemed that this race could have no end.

Eventually we invented a new idea, to justify a situation we really couldn't do anything about: Mutually Assured Destruction (MAD). We didn't dare try to bomb Russia, because we knew that Russia would respond quickly and thoroughly, destroying us. We hoped that Russia understood that we could also respond quickly with enough firepower to totally wipe them out. As it turned out, they did realize this. Thankfully, MAD did not actually ensure any destruction.

Obviously, MAD is not really a good idea -- it is the idea that no one can win. It is a strong commentary on the state of the world when developing the plan that "everyone will die" is a good solution. We are mostly past that; MAD is enough a part of the world's understanding of international politics that first-world countries no longer see it as profitable to actively threaten each other.