NEW YORK, Sept 20: China and the United States are divided on many issues, from tariffs and technology to Taiwan. But there is one thing tying them together: fast food.American restaurant and beverage chains are expanding rapidly in China, drawn by the potential customer pool in a country with four times the US population.China's languishing economy and cutthroat industry competition, meanwhile, have Chinese chains trying their luck in the US, turning crumbs and straws into a two-way cultural bridge between the two superpowers.The bilateral trade in burgers and bubble tea is business- and consumer-led gastrodiplomacy in action, said Yaling Jiang,…