Where other nations disbanded their empires following the second world war, America’s underwent transubstantiation, from something solid to something more ethereal. It became a shorthand, connoting an amorphous global entity and its quasi-imperial depredations: commercial infiltration, cultural indoctrination, fomenting coups, waging war. Suitably, this construct (Coca-Cola and cruise missiles) acquired a ‘logo’, writes Daniel Immerwahr — the silhouette of the continental United States sitting athwart the northern half of the Western hemisphere, as iconic as Nike’s swoosh; on the map at least, minding its own business.