Now, what happens when two enemy nations both have nuclear weapons? Essentially nothing. Since either country could destroy the other, the concept of Mutually Assured Destruction takes over to prevent major conflict. But one nuke isn't enough to deter an attack. A nuclear nation needs to have enough weapons on hand to ensure mutual annihilation by stocking up on so many nukes that they couldn't all be destroyed at once by a surprise first attack. This is called "second strike capability" and is the reason why the United States and Russia still possess an almost absurd amount of nuclear weapons (enough to destroy the world many, many times over).

It may seem like a paradox, but there is strong evidence that nuclear weapons have actually helped decrease the number of major conflicts in the world. This certainly seems plausible to help explain the relative global peace of the past several decades, but many scholars of international relations are concerned about what happens to a nuclear state when the "State" no longer functions. One of the primary worries regarding North Korean or Iranian nuclear weapons is that these are inherently unstable regimes. If the regime collapses while it still holds nuclear weapons, what happens? Mutually Assured Destruction assumes that all actors are rational people (i.e. not crazy people who want to destroy the world). Though it remains ridiculously hard for terrorists to obtain nuclear weapons, the thought of a nuclear nation falling apart in a political sense remains a very serious problem.