In Shanghai, on December 11, 2019 — just weeks before a mysterious virus would be discovered 500 miles to the west — more than 10,000 people crowded into the National Convention Center’s large dark hall. As the crowd waited for Eric Broussard, Amazon’s vice president of international marketplaces and retail, to make his keynote address, the screen over the stage projected the gathering’s slogan: “A World Without Boundaries.” It was the annual “Cross-Border Summit for Amazon’