With Putin’s threats in Ukraine, China’s accelerated weapons programme and the US’s desire for superiority, what will it take for leaders to step back from the brink?

Like Toto in The Wizard of Oz, at their 1985 summit in Geneva President Ronald Reagan and the Soviet leader Mikhail Gorbachev pulled back the curtain to reveal the truth behind the terrifying spectre of nuclear war, which their countries were spending hundreds of billions of dollars to prepare for. “A nuclear war cannot be won,” they jointly stated, and “must never be fought.” They omitted the inescapable corollary of those first six words: a nuclear arms race also cannot be won.

Still, the statement, almost unique among government declarations for its blunt truthfulness, strengthened the case for the arms control and nonproliferation undertakings that followed. Decades of agonisingly difficult negotiations built up a dense structure of treaties, agreements and even a few unilateral moves dealing with offensive and defensive nuclear weapons of short, medium and long range, with provisions for testing, inspections and an overflight regime for mutual observation. Often the two sides would only give up systems they no longer wanted. Frequently the language of the agreements was the basis of future friction. On the US side, the political price of securing Senate ratification of treaties could be extremely high.