As the U.S. and China steam toward a full-fledged trade war, American casinos across the world could become collateral damage. Since 2012, mainland China has been the largest source of international travel and travel spending, and Beijing has become increasingly adept at harnessing these globetrotters as a form of economic diplomacy, rewarding friends and punishing enemies. Ominously, this trade war approaches amid looming expiration of casino concessions in Macau, three of them controlled by American companies.