I was in London on the afternoon of Sept. 11, 2001, a day when strangers in shops, hearing my American accent, offered their cell phones in case I wanted to call home. That evening, parties were cancelled. The next day, political events were called off. An American friend who lives in London received a condolence card from his neighbors, whom he’d never met—and he was not alone. Overwhelmingly, the first British reaction to the terrorist attacks on Washington and New York was deeply sympathetic, and profoundly pro–American.

But so were the reactions of many others, across Europe and around the world. Several days after September 11, I left London and returned to Poland, where I was then living. That evening I attended a concert in a provincial city. In the foyer of the symphony hall, someone had put up a large American flag and surrounded it with candles. At the start of the concert, the conductor announced that there would be a change: Instead of the planned program, the orchestra would play only Mozart’s Requiem, in honor of the 9/11 victims. These decisions were completely spontaneous and utterly apolitical: No one had reason to think that there would be even a single American in the audience. Within a few days, of course, a second reaction had set in. In London, a television studio audience attacked the former American ambassador on the air, accusing the United States of provoking international hatred and therefore bearing responsibility for the attacks. The New Statesman, an influential British left–wing magazine, ran a cover story, saying more or less the same thing. “American bond traders, you may say, are as innocent and undeserving of terror as Vietnamese or Iraqi peasants,” the editors wrote. “Well, yes and no.... If America seems a greedy and overweening power, that is partly because its...