One lesson from recent economic troubles has been the usefulness of history. Just as the crisis was unfolding, the Harvard economists Carmen Reinhart and Kenneth Rogoff — who unfortunately became famous for their worst work — published a brilliant book with the sarcastic title “This Time Is Different.” Their point, of course, was that there is a strong family resemblance among crises. Indeed, historical parallels — not just to the 1930s, but to Japan in the 1990s, Britain in the 1920s, and more — have been vital guides to the present.