Benjamin Disraeli described the Franco-Prussian War that brought about Germany's unification in 1871 as "the German revolution, a greater political event than the French." It turned out to be a shrewd claim, given the two world wars that followed. But the German reunification of 1989 seems less a revolution in Disraeli's sense than a restoration. Rather than setting into motion yet another round of great-power rivalry, the end of Germany's division brought about changes that extended democratic stability through Eastern and Central Europe. That Europe is no longer a flashpoint in world politics is a measure of just how...