The foundations of America’s relationship with China crumbled last week. The key developments were a lurch by the US towards protectionism and a swing by China towards one-man rule.

For the past 40 years, the world’s two largest economies have both embraced globalisation, based on understandings about how the other would behave. The Chinese assumed that the US would continue to support free trade. The Americans believed that economic liberalisation in China would eventually lead to political liberalisation.

Both of these assumptions are now shattered. On Sunday, China’s National People’s Congress rubber-stamped a constitutional change that would allow President Xi Jinping to rule for life. Three days earlier, President Donald Trump announced tariffs on steel and aluminium and tweeted that “trade wars are good and easy to win”.