Will the dollar stay dominant?

A MILE FROM the White House stands the Capital One Arena, a 20,000-seat stadium for basketball and ice-hockey games. The arena is in the Chinatown district of Washington, surrounded by Chinese restaurants and the “Friendship Archway”, built to celebrate the American and Chinese capitals becoming sister cities in 1984. One afternoon in March, this correspondent arrived at the arena and went to buy a Diet Coke from the Walgreens opposite. Once at the till she tapped on the azure blue Alipay app: up popped a QR code, scanned by the checkout worker to collect payment. The transaction took a second.

Had it been possible to enter the stadium it would have been just as easy to use Alipay, the payment platform started by Alibaba, to buy tickets or snacks. Nor is the Walgreens in Chinatown unique in accepting the app. Around 7,000 of them across America take it, as do shopping centres like Pier 39, in San Francisco, and several Chinese restaurants in New York and Boston.

These merchants want to make shopping easier for Chinese tourists, not to persuade Americans to use Alipay. The payment app is not easy for English-speakers (even in “English” mode most of the interface is in Chinese characters, so non-natives need screenshots reliant on Google translate). But its growing acceptance outside China, where Alipay and its rival...