Surprise U.S. tariffs. A war involving Iran. New American tech bans and Chinese export controls. The list of geopolitical shocks that CEOs must be mindful of, let alone plan for, keeps getting longer. “We’re in a world where all the assumptions about international institutions, free trade, a rules-based order—that’s all going away,” said Dominic Barton, strategic counselor to Eurasia Group and chair of Australian mining giant Rio Tinto. Barton spoke with Fortune days after U.S. President Donald Trump imposed 50% tariffs on some Canadian goods including autos, dairy, and alcohol. The president had also threatened tariffs in response to wildfire...