Millions of mines, cluster bombs and unexploded ordnance still litter the Cambodian countryside, a direct result of decades of conflict stemming from the Vietnam War.

Phnom Penh is a close partner of China, which has invested billions of dollars in projects including roads and airports, and is the country’s largest creditor.

As President Donald Trump’s trade war locks the world’s two largest economies on a collision course, America’s unnerved ...