The NPT today is an object of ambivalence among realists. It has not always been, however. At the start, realists had the insight that stability is the sine qua non of security in an age of nuclear-armed powers, and the realists’ insight inspired states to draft the NPT the way they did. States drafted the NPT to avoid a worst-case outcome— an escalating rivalry between nucleararmed states from which they would never escape. Article VI of the NPT, by requiring that states pursue a negotiated settlement of the challenges of nuclear arms, ensured that states preserve the chance to arrest the rivalry. By placing the emphasis on the elusive goal— effective measures to achieve arms control— Article VI, moreover, pledged states to negotiate arms control agreements that might actually work in the world as the world exists.

Realists resiled from the NPT when they began to perceive that the prescriptions that disarmament activists were drawing from the NPT would impede a rational and security-minded approach to nuclear arms control. The NPT, however, is no longer the only treaty that affects nuclear arms control.

We live now in a world of two treaties. On January 21, 2021, the eve of entry into force of the TPNW, the Lord Bishop of Coventry speaking in the UK House of Lords said that ‘as of tomorrow the TPNW will be no less a reality for the UK than for countries that support it.’ He forecast that the TPNW's ‘underlying humanitarian motivations will loom large over any future discussion of our non-proliferation responsibilities.’ As a matter of international law, to a country that is not party to a treaty, the treaty is less a reality than to a country that is, but the Lord Bishop was not making a lawyer's point. The TPNW has attracted the support of the disarmament community and of many governments. If the support continues to grow, then the TPNW soon will be the focal point of discourse on nuclear weapons. It will ‘loom large’ over any effort to revive negotiations on nuclear arms control.

I have argued in this book that we should take the TPNW seriously, for it augurs a new era in security diplomacy. A TPNW era will not be congenial to the interests of the US, its allies, or like-minded countries.