The dominance of the U.S. dollar, currently used in roughly 80% of international trade finance, has historically given Washington a big advantage in policing global business. Most international transactions denominated in U.S. dollars must be settled by American banks, giving Washington the ability to monitor them—and cut off users’ dollars if necessary, crippling their operations. But when U.S. adversaries use yuan to run their businesses, the transactions don’t enter the U.S.-led banking system, neutering Washington’s powers.