Beijing’s move this week to add 20 more Japanese entities to its export-control list is the latest chapter in a complex US-Japan-China geopolitical triangle. Over the past seven months, an angry China has punished Tokyo repeatedly. A miffed Japan is left feeling betrayed. And a war-distracted Washington has struggled to navigate between the two, adding further tension in a region already on tenterhooks, according to analysts and former US government officials. The gnawing unease was sparked in...