There is a pervasive consensus that the post-1945 distribution of power differed in fundamental ways from that which had preceded it. The war severely weakened the traditional powers of Europe and the defeat of Germany was to be succeeded by a temporary, and then enduring, partition of the country. Soviet power had been injected into the heartland of Eastern Europe, at the same time as the United States emerged as the world's foremost economic and technological power.

This postwar order was immediately to be shaped by the twin consequences of the war and of the developing Soviet–American antagonism. Whether that order was the product of aggressive Soviet expansionism, as the traditional Cold War historians would have it, or of a dynamic American capitalism relentlessly pursuing ‘Open Door’ policies, as the revisionists retorted, or, indeed, whether the Cold War was simply the inevitable structural by-product of the vacuum in postwar Europe, it is certainly the case that more so than in most periods, it was to be the relationship between two dominant states that was to lend the era its characteristic features: to understand the post-1945 order, we need to understand the dynamic superpower relationship.

There is a danger with this period, as with the others, in describing it as if its dominant features persist unchanged throughout several decades.