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For her first overseas trip as secretary of state, Hillary Clinton went to Asia. For his first trip, John Kerry chose Europe. His choice is partly a result of his strong connections across the Atlantic and partly a move against the frustrations U.S. diplomats have faced in places like Beijing. Kerry’s choice also speaks to a remarkable narrowing of the Atlantic, which culminated in Obama’s championing of a transatlantic free-trade agreement in his State of the Union address this month. Only 10 years ago, Europe and the U.S. were meant to be so different that not only did they have different views, but they viewed each other as if from different planets. Politically and militarily, the author Robert Kagan claimed, Americans were from Mars and Europeans from Venus. American...