To hear Maureen Footer tell it, Paris in the late 1940s mirrors America of late. “Society was polarized, people felt like they were losing their identities, and outside influences threatened what was considered the French way of life,” the style historian says on the eve of publishing her new book, Dior and His Decorators: Victor Grandpierre, Georges Geffroy, and the New Look (The Vendome Press, $60). But instead of snarking on Twitter, she continues, couturier Christian Dior and two friends—the charming Grandpierre, a former photographer; the melancholic Geffroy, an ex–fashion designer—went about making French classicism great again, though they stirred in English furniture, Finnish carpets, and Middle Eastern bronzes. The modish result was revolutionary, Footer says, “in a streamlined but cosmopolitan manner that answered, as design often can, the big…