The Berlin Wall was the symbol of the Cold War, of Europe’s division, and of the Communist challenge to human freedom. That it became so pivotal was the result of one of the anomalies of the postwar settlement. The joint occupation by the four victors—the United States, the Soviet Union, Great Britain, and France—of Germany’s capital, located ninety miles inside the Soviet zone of occupation, grew out of the wartime illusion of continued Allied cooperation in the governance of defeated Germany.

The premise was bound to be unfulfilled. Stalin saw in victory an opportunity to combine historic Russian imperialism with Communist ideology and insisted on installing Soviet-style governments in what he treated as Russia’s sphere in Central and Eastern Europe up to the Elbe River. The principal states in that region—Poland, Hungary, Czechoslovak ...