Rebecca Johnson, internationally recognized expert on nuclear disarmament and nonproliferation, is director of the London-based Acronym Institute for Disarmament Diplomacy, vice president of the Campaign for Nuclear Disarmament and former cochair of the International Campaign to Abolish Nuclear Weapons.

A schoolgirl's charred blouse and a child's melted lunch box in the Hiroshima Peace Memorial Museum brought home to me the realities of nuclear war. It was 1981, and I was a young teacher in Tokyo. Tears welled up as I felt a deep, visceral understanding of the horror of that bright August morning, when the "Little Boy" bomb incinerated a city full of people. I vowed that such inhuman weapons must never be used again.

A year later, I was back in Britain and getting involved in mass protests against a new generation of nuclear weapons. Invited to speak in Hiroshima and Nagasaki in August 1983, I was by then a feisty, determined peace activist, living at the Greenham Common Women's Peace Camp where NATO planned to deploy the first cruise missiles in Europe.

Having recognized the inhumanity of nuclear weapons and war, I felt impelled to become an active peace campaigner. As a scientist, I researched the effects of nuclear detonations, blast, burns, radiation and nuclear winter. I also analyzed governmental justifications for nuclear weapons. Amazed by the flaws and irrationality embedded in nuclear doctrines, I felt that this was too important to leave up to politicians and militaries who had a vested interest in keeping nuclear weapons going. Their pro-nuclear assurances were unconvincing, especially as so many retired leaders confirmed our arguments about the risks and insecurities inherent in nuclear policies.

Taking to heart the feminist recognition that "the personal is political," I put my career on hold and worked determinedly for disarmament and human rights. With millions calling for nuclear disarmament, Presidents Reagan and Gorbachev signed the Intermediate-Range Nuclear Forces (INF) Treaty in December 1987. This groundbreaking treaty banned and eliminated the ground-launched cruise missiles from Greenham Common, together with Pershing and SS-20 missiles from across Europe and Russia.

That success gave me an inspiring taste of what we could achieve if we worked globally. The INF Treaty enabled changes that brought the Berlin Wall down. That showed me the dynamic power of multilateral disarmament strategies—involving nonviolent activists, academics, diplomats, faith leaders, elected representatives and willing states, creating conditions to bring reluctant governments to act in accordance with international agreements. By 1988, I was working with campaigners, nuclear test victims, parliamentarians and governments to realize another treaty that would end another humanitarian obscenity. The long-sought Comprehensive Nuclear-Test-Ban Treaty was concluded in 1996. It was an important achievement, but carried sobering lessons. Government negotiators overloaded the treaty with technical and political conditions that reduced its chances of entering into force. If our objective is genuine disarmament, it is not enough to make partial bans that allow the nine nuclear-armed states to keep modernizing their nuclear weapons in perpetuity.

To prevent proliferation and eliminate nuclear arsenals, we need to unequivocally prohibit nuclear weapons, thereby taking away their political status and value. When a nuclear-ban treaty is in place, the nuclear-armed states will have to stop modernizing their arsenals and undertake genuine steps to fulfill disarmament obligations. History shows that an active, inclusive campaign like the International Campaign to Abolish Nuclear Weapons (ICAN) must work with all nations—possessors and non-possessors—as we all have responsibilities to initiate and negotiate disarmament treaties.

It has been 70 years since atomic bombs incinerated Hiroshima and Nagasaki. If we do not want this to happen again, we must bring about a universally applicable treaty that clearly prohibits the use, deployment, development, production, stockpiling and transfer of nuclear weapons and devices, requiring and leading to their total elimination. If not now, then when? If not us working together, then who? A nuclear-ban treaty has to be the next step toward our future security in a world without nuclear weapons.