One might begin, like a well-heeled traveller, in that luxurious Manhattan hotel the Waldorf Astoria. In December 1900, in the last weeks of Queen Victoria’s reign, a twenty-six-year-old journalist, Winston Churchill, just elected to parliament, lectured there on the Boer War. It was still raging, and he was introduced by an ageing author called Mark Twain, who disapproved of it. Mindful that the young war-hero had an American mother, Twain joked about the Anglo-American tradition. “We have always been kin,” he told his New York audience, “kin in blood, in religion, in representative government, in ideals.” But the Spanish-American War…