As a result of the expiration of the START Treaty on February 5, 2026, without an extension, Russia and the United States for the first time since the end of the cold war have dived into a legal vacuum – without agreed mutual restrictions on the most destructive weapons in history, which can destroy modern civilization within a few hours. The predictable mutual buildup of nuclear warheads, combined with Trump's announced “Golden Dome” space-based anti-missile defense, will definitively undermine strategic stability by increasing the incentives for a first nuclear strike. Combined with the widespread introduction of artificial intelligence in combat command and control systems of nuclear forces, this is fraught with unpredictable consequences. The end of the START dialogue is likely to spur destructive processes throughout the broader nuclear arms control system. First, this applies to the Comprehensive Nuclear Test Ban Treaty (CTBT), the collapse of which would undermine the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), with a domino effect on other agreements in this area. It is hardly justified to attribute the origins of the present crisis to the emerging multipolarity of the world order or the latest military technologies. Rather, the roots of the crisis lie in the changed psychology of the ruling circles of a number of leading powers. What is badly needed now is a profound revision of the perception of nuclear weapons as an effective instrument of foreign policy and warfare among the new political elites. The main practical task in the near future is to preserve the two remaining basic elements of nuclear arms control: the CTBT and the NPT. This is important in and of itself and for creating a favorable legal environment for restoring dialogue on strategic offensive arms. In future START negotiations, it would be reasonable to start moving not “in depth”, by reducing arsenals further, but “in breadth”, by covering adjacent areas of strategic stability and the forces of third nuclear-weapon states. The revival of the treaty-based limitation system in the field of nuclear and other arms is an indispensable condition for the survival of human civilization in the 21^st century.