The Historian Who Influences Both Obama and Romney

One thing Barack Obama and Mitt Romney seem to have in common these days is an appreciation for the neoconservative historian Robert Kagan.

The Romney campaign has retained Mr. Kagan as a foreign-policy adviser, and according to news reports, President Obama has read and been influenced by a recent Kagan essay in The New Republic, which addresses “the myth of American decline” and underscores the importance of the United States’ maintaining its “global responsibilities.”

That essay was based on Mr. Kagan’s new book, “The World America Made,” a book that turns out to be a much more scattershot affair than the magazine article, a book that undermines its more potent arguments with fuzzy generalizations, debatable assertions and self-important declarations of the obvious (“It is premature for us to conclude, after ten thousand years of war, that a few decades and some technological innovations would change the nature of man and the nature of international relations.”)

The book does make a strong case for the notion that “the most important features of today’s world — the great spread of democracy, the prosperity, the prolonged great-power peace — have depended directly and indirectly on power and influence exercised by the United States,” and suggests that “when American power declines, the institutions and norms American power supports will decline too.”...