BERLIN — Just 20 years ago, German lawmakers hunkered down for a passionate 10-hour debate to make a decision that seemed as momentous as it was a no-brainer: Should the capital of the newly reunified country remain where it was — in Bonn on the Rhine — or move back to its historic, eastern location on the Spree, amid the monuments and mixed memories of Berlin?...

[I]n 1991, Bonn’s provincialism seemed a plus, not a minus. Some Germans believed that a move back to Berlin — the old imperial capital, Hitler’s capital — would coax forth the ghosts of Prussian militarism, of centralized rule after decades of federalism that had assuaged the fears of neighbors to the east and the west and of Germans themselves. Worse still, the argument went, the blossoming of Berlin as the capital of reunified Germany would spell stagnation for poor Bonn.

So when the vote came down — 337 for Berlin and 320 for Bonn — it seemed surprisingly narrow and, most of all, counterintuitive. Yet, since then, virtually every other cataclysmic forecast has been just as wrong.

“There has been no new Wilhelm-ism,” wrote columnist Eckhard Fuhr in Die Welt, referring to the last German emperor, Kaiser Wilhelm II, “and the centralized castration of German federalism has not happened.”...