New York

AMAZON'S plans to open as many as 400 brick-and-mortar bookstores, revealed on Tuesday by a mall executive, may seem an unlikely turn of events. But should Amazon proceed, it will have plenty of company.

In recent years, a rash of e-tailers from Warby Parker to Bonobos have opened stores. Some are pop-ups, but others are designed to be permanent. Three key forces are driving this trend. Malls, keen to find new tenants as struggling traditional retailers close stores, see online merchants as potential traffic drivers. E-tailers have discovered that a physical location helps consumers discover their brand. Traditional retailers, meanwhile, are buying or partnering with online merchants and opening boutiques inside their stores.