Unchecked nuclear weapons development in North Korea and the incipient nuclear weapons programme in Iran currently pose seminal challenges to the Nuclear Non-Proliferation Treaty (NPT). The disposition of these cases may determine the future of the NPT and will shape non-proliferation and disarmament efforts for the next decade or more. This article assesses these two challenges, focusing on the actions concerned European states might take to leverage and guide the inevitably central US role. The article concludes that, by smoothing the sharper edges of US nuclear and strategic policies, European states can promote political conditions more favourable to non-proliferation solutions in both critical cases and help reduce reliance on nuclear weapons threats in global security relations more broadly.