Recalling why U.S.-Russian nuclear cooperation was essential during the late 1980s, Russia’s then-First Deputy Minister of Atomic Energy Lev D. Ryabev said: “We arrived in the nuclear century all in one boat—a movement by any one will affect everyone… [Russian and American nuclear scientists] were doomed to work on these things together, which pushed us toward cooperation.”

Russia mattered then and it matters now. Today, like 30 years ago, the size of its nuclear program—namely its nuclear weapons, facilities, materials, experts—and its safety, security and environmental challenges are rivaled only by the United States. They dwarf all others in the world combined.

The dangerous difference between then and now is that the hard-won cooperation that amazingly prevented nuclear weapons, materials and technologies from spilling out of the disintegrating Soviet empire and into the hands of actors bent on deploying them has been replaced with animosity, tension and a freeze on substantive collaboration. Within the past month two U.S.-Russian agreements—on plutonium disposition and on cooperation in nuclear- and energy-related scientific research and development—have been suspended. Another one—on conversion of Russian research reactors—has been terminated altogether. Meanwhile, officials in Europe and the United States have tracked a number of disturbing activities suggesting that the Islamic State and its sympathizers may be pursuing nuclear and radiological terrorism as the group has been pushed on the defensive.

I must add that Russia also matters to me personally: It has been inextricably intertwined with my life. I was born during World War II in Europe. My father, a conscript in the German army, never returned from the Russian front. I grew up in post-war Austria, which until 1955 was under divided Allied and Soviet occupation. In 1956, I immigrated to the United States with my mother and siblings.

For the first 20 years after I received my bachelor’s degree in metallurgy and materials science from Case Institute of Technology in 1965, Russia also mattered because I spent most of that time employed at the Los Alamos National Laboratory. Our job was to deter the Soviet Union, which was in intense ideological, economic and military competition with the United States.

I became director of the laboratory in 1986 shortly after Mikhail Gorbachev took over leadership of the Soviet Union and dramatically changed geopolitics with his outreach to U.S. President Ronald Reagan and the West. At the end of 1991 the Soviet Union dissolved into 15 independent states. Remarkably and unexpectedly, the Cold War was over.

Mutually assured destruction was replaced by an acknowledgement of mutual nuclear interdependency. The West, rather than being threatened by the enormous nuclear might in the hands of Soviet leaders, was now threatened by Russia’s weakness and the potential for its new government to lose control of the nuclear assets it had inherited from the Soviet Union. The safety and security of Russia’s nuclear assets—its tens of thousands of nuclear weapons, over a million kilograms of fissile materials, a huge nuclear infrastructure and some one million employees of the once-powerful Soviet nuclear establishment—posed an unprecedented risk for Russia and the world.

Fortunately, collaboration replaced confrontation 25 years ago. President George H.W. Bush reached across the political divide to lend a helping hand during times of Soviet political and economic chaos to help Moscow manage its huge nuclear complex. Senators Sam Nunn and Richard Lugar pioneered the visionary landmark Cooperative Threat Reduction legislation (appropriately called Nunn-Lugar) to provide rationale and financial support to that helping hand. The nongovernmental community—led by academics at U.S. universities, foundations such as the Carnegie Corporation of New York, groups such as the Federation of American Scientists, the U.S. National Academies and the Natural Resource Defense Council—paved the way by reaching out to courageous Soviet/Russian organizations, such as its Academy of Sciences and other leading thinkers.

The role of the American and Russian nuclear weapons laboratories changed as well. They had become acquainted during the 1988 Joint Verification Experiment, underground nuclear tests conducted at each other’s nuclear test sites with on-site monitoring by the other side to develop confidence in nuclear test verification so as to facilitate ratification of the Threshold Test Ban Treaty, which had lingered unratified since its signing in 1974. That acquaintance and subsequent interactions at the Geneva TTBT negotiations prompted both sides, but led by the Russian nuclear weapons scientists, to push their governments to allow scientific collaboration between former adversaries.

In February 1992, less than two months after the dissolution of the Soviet Union, Washington and Moscow approved exchange visits of the directors of their nuclear weapon design laboratories: Vladimir Belugin, director of the Russian Federal Nuclear Center VNIIEF, and Vladimir Nechai, director of the Russian Federal Nuclear Center VNIITF, visited the Lawrence Livermore and Los Alamos national laboratories; John Nuckolls, director of LLNL, and I, director of LANL, visited the formerly secret cities of Sarov and Snezhinsk, home to VNIIEF and VNIITF, respectively.

Those visits marked the beginning of a remarkable period spanning more than two decades of scientific and technical nuclear cooperation that we called lab-to-lab cooperation—the story told in a book called “Doomed to Cooperate” by dozens of Russian and American scientists, engineers and officials. The book demonstrates how the camaraderie and the interpersonal relationships among the scientists and engineers helped them overcome the radically different views of the nuclear challenges as seen by the two governments.

To the U.S. government, Russia’s nuclear complex was considered an inheritance from hell: the danger of loose nukes, loose nuclear materials, loose nuclear experts and loose nuclear exports. The Russian government considered its nuclear complex part of its salvation in that it would provide a basis to help the country achieve a competitive, modern industrial base and economy. In “Doomed to Cooperate,” we, the scientists and engineers, describe how we confronted the unprecedented safety and security challenges, and how we collaborated to discover new science and help Russia’s vastly oversized nuclear workforce use their talents in civilian and commercial pursuits.

Russia’s nuclear complex has mattered enormously over the past 25 years. It has survived the four nuclear dangers mentioned above to a large extent because of the Russian nuclear community’s dedication, professionalism and patriotism—and their ability to persevere during difficult times. But it also had the benefit of innovative U.S. government programs, collaborations championed by U.S. NGOs and the many hundreds of nuclear lab-to-lab collaborations. These efforts helped the huge Soviet nuclear complex transition those in Russia and several other former Soviet republics in a safe and secure manner.

Unfortunately, whereas a convergence of our governments’ interests immediately following the end of the Cold War allowed for innovative nuclear cooperation, growing political differences during the past 10 to 15 years have done the opposite. The current differences over Crimea, eastern Ukraine and Syria have all but brought meaningful nuclear collaboration to an end.

Yet, Russia continues to matter—and cooperation between Moscow and Washington on common nuclear challenges is essential. They must take steps to reverse what appears to be a return to an arms race and potential nuclear confrontation. They must continue to share experiences and best practices to keep their huge nuclear complexes safe and secure. Although Russia has made enormous improvements in these areas, lessons from the United States nuclear complex demonstrate that this job is never done. Together, Moscow and Washington have a greater stake than anyone in ensuring that the nuclear nonproliferation regime is strengthened rather than crippled. And more than anyone in the world they have a responsibility to join their technical, professional and military talents to help the world avoid nuclear terrorism.

The stakes couldn’t be higher: Russia matters; nuclear cooperation is essential; isolation invites catastrophe.