SYDNEY • To understand why the Trump administration has struggled to build a global coalition of allies in its trade war with China, it helps to understand what is happening in the rolling hills and valleys of Australia's south-east and south-west coasts.

Vineyards that once made many crisp white wines and fruity red ones popular with American buyers are now also producing more austere reds, favoured by a segment of a rapidly expanding market of Chinese drinkers.