How Amazon turned the whole month of July into a shopping holiday

Branded is a weekly column devoted to the intersection of marketing, business, design, and culture. Of all the ways to measure the success of Amazon’s Prime Day event—its yearly mid-July onslaught of limited-time, members-only deals and markdowns, which just concluded its 10th record-setting iteration—the most remarkable may be the copycats. What was once a blah stretch on the retail calendar is now a promotional shopping carnival. Just before Prime Day this year, archrival Walmart...