Going to war against Iran promised to change the Middle East by weakening a villainous regime and thwarting its nuclear ambitions. To its most bullish supporters, the war would also change the world by cowing an ascendant China. It would show how America’s control over the flow of oil leaves China vulnerable. And it would boost deterrence by contrasting America’s military supremacy with China’s reluctance or inability to save its friends. A month into the fighting, this logic still seems misguided and hubristic. Certainly, that is the way it looks from Beijing.  The Economist  has been speaking to diplomats, advisers, scholars, experts and current and former officials in China. Almost all of them see the war as a grave American error.…