Disarmament remains a contested topic within the nuclear weapons debate and it is included as one of the mutually reinforcing pillars of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). However, when the Treaty on the Prohibition of Nuclear Weapons (TPNW) was mandated by UNGA in 2016 and later entered into force in 2021, it was immediately rejected by all nuclear-weapons states – China, France, Russia, the UK and the US – and their allies. The paradox of such a negative response to the new treaty despite their alleged loyalty to the disarmament pillar of the NPT was the starting point of the thesis and was examined through the theoretical lenses of constructivism, neo-liberal institutionalism and structural realism to pinpoint which offered the most tangible answer to the question at hand. The research was conducted by utilizing the method of qualitative content analysis on statements and working papers by the five nuclear-weapons states, and it concluded that – while all theories brought up interesting points – structural realism provided the most useful perspective on the matter through its take on states’ insecurity towards each other