At a conference in Switzerland in 2011, I bumped into an old friend, Gideon Rachman of the Financial Times, whose writings on global affairs had taken a pessimistic turn. Why, I asked, are you so gloomy? He replied that he wasn’t as gloomy as all that. “You have literally just written a book called ‘Zero-Sum World’,” I said. “Fair point,” he conceded. 

As Donald Trump and Xi Jinping prepare for a summit in Beijing, the kind of zero-sum thinking that Gideon was complaining about 15 years ago is even more rampant in high places. Mr Trump seems to think diplomacy is about him winning and others losing. Mr Xi is more subtle, but appears to see most American losses as gains for China. As our cover leader this week argues, the two men’s obsession with dominance means they are failing to co-operate sensibly in areas that could benefit both their own countries and the world. 

The most urgent is artificial intelligence, which could pose an existential danger to humanity by enabling bioterrorists to create superweapons. America and China are the two countries that matter when it comes to AI. Both acknowledge the risks. But they should be doing more to agree on guardrails for fear of ceding an advantage in the race to AI supremacy. 

On climate change, another problem crying out for global collaboration, Mr Trump favours inaction and China once broke off talks because an American politician had visited Taiwan. As for the Middle East, nearly everyone would benefit from a re-opening of the Strait of Hormuz, but China is content to let America reap the fruits of its own mistakes, and has been slow to use its leverage over Iran to restore the flow of oil on which China, too, depends. 

Much of next week’s summit will focus on trade, where each side has the power to hurt the other badly and an unstable truce prevails. China may play on Mr Trump’s fixation on America’s bilateral deficit to tempt him to sell out Taiwan by offering concessions on trade. He should not take the bait. All in all, it is hard to be optimistic about the summit: the superpowers are not so much leading the world as holding it to ransom.