The hardest problem is not the existence of nuclear weapons but the degradation of the shared framework within which their deterrence function operates.
The theory of nuclear deterrence rests on a set of assumptions about rationality, communication, and the stability of the actors involved. Those assumptions were always contestable. They are now under greater stress than at any point since the cold war period of maximum doctrinal anxiety.
The fundamental premise is that nuclear weapons deter their use through the credible threat of retaliation. This logic held — more or less, with significant moments of near-failure — for seven decades. But the logic of deterrence is not self-enforcing. It depends on the shared understanding that thresholds exist, that crossing them has predictable consequences, and that the parties involved have sufficient rationality and institutional stability to manage the communication that deterrence requires.
Several of these conditions are now less secure than they were. The number of nuclear-armed states has grown. The proliferation of precision conventional capabilities has blurred the threshold between conventional and nuclear use — particularly for states that rely on nuclear weapons to compensate for conventional inferiority. The doctrinal assumptions of major powers have diverged in ways that create dangerous ambiguity about what each considers escalatory.
The hardest problem is not the existence of nuclear weapons but the degradation of the shared framework within which their deterrence function operates. Arms control architecture has largely collapsed. Channels for crisis communication have atrophied. The strategic cultures of major nuclear powers are increasingly opaque to each other.
Deterrence is not dead. Nuclear weapons still deter. But the conditions under which deterrence operates are more fragile than the stability of recent decades suggests. The threshold that nuclear doctrine defends is a political and psychological construct, not a physical one. Maintaining it requires active work that the international system is currently not doing.