When they sat down with President Franklin Roosevelt in 1943 for the first Big Three conference of World War II, Britain's Prime Minister Winston Churchill and Soviet leader Joseph Stalin presented a striking study in contrasts: one a patrician, the other a peasant; one a democrat, the other an autocrat; one colorful and expansive, the other secretive and terse.
The British and Russian leaders differed in one other respect as they joined Roosevelt in Tehran to fine-tune Allied strategy to defeat Nazi Germany. As a leading Stalin biographer records, Churchill came to the table with an empire to lose, and Stalin with an empire to gain - which, in fact, is precisely what happened.
Though noticed at the time by few besides Churchill and Stalin, the fierce struggle to liberate Europe and Asia from fascism was setting the stage for changes that were destined to shift the global balance of power in the postwar era.
The defeat of Germany, predictable by 1943, would help to create a power vacuum in Central Europe that would be filled by the Red Army and, after the war, by a collection of Soviet puppet regimes: the empire Stalin had to gain.
The ideals of liberty and self-determination propagated by the Allies during the war, meanwhile, would nourish successful independence movements in England's far-flung colonies after the war: the empire Britain had to lose.
Such imminent developments were scarcely envisioned in the euphoria of Aug. 14, 1945, the day millions of jubilant, war-weary people poured into streets and public squares around the world to celebrate the surrender of Japan - the final act of World War II.
As it happened, these political shifts were just two of the extraordinary changes wrought by a war that has proved to be a sharp dividing line between two worlds, politically, culturally, socially, and militarily.
Before World War II, Europe was supreme in world politics. After the war, political and military power gravitated from an exhausted and decimated Europe westward to the United States and eastward to the Soviet Union.
Before the war, military force was an acceptable extension of diplomacy. After the war, nuclear weapons made war unthinkable, if not entirely unlikely.
Before the war, Asia and Africa were dominated by colonial powers. After the war, the European empires - the French, Dutch, and Belgian as well as British - were swept away in a tide of nationalism and communist ideology.
Before the war, barely 60 nations dotted the globe, only a dozen of which were politically consequential. Since the war, more than 125 new nations have been added to the map, the smallest of which wield disproportionate influence in an international system democratized by the creation of the United Nations - itself a legacy of six years of global conflict.
Before the war, Eastern Europe was made up of ethnically heterogeneous states. After the war, it was composed of ethnically homogeneous states, purged of minorities by the massive ethnic cleansing that, among other things, eliminated Jews from Poland, Germans from Czechoslovakia, and Poles from the Soviet Union.
"What is happening in Bosnia today is an extension of what happened during World War II in places like Poland, Czechoslovakia, Byelorussia, and Ukraine," notes University of Chicago political scientist John Mearsheimer.
Together, the forces unleashed by World War II delivered the final blow to a political order whose foundations had been set three centuries before, in the Treaty of Westphalia. The treaty created the European state system.
Since the war, a unipolar world with Europe at its center has given way to a bipolar world dominated by the US and the Soviet Union and, more recently, to a multipolar world in which a resurrected Japan and Europe have become leading centers of global power.
The war, which claimed 55 million lives, also had vast domestic implications for the US. The productive energy and massive federal expenditures needed to mount a sustained war against Germany and Japan transformed every aspect of American life.
To turn the US into what President Roosevelt called an "arsenal of democracy," the Roosevelt administration and Congress hiked annual military expenditures from $2 billion to $85 billion in the four years between Pearl Harbor and V-J Day. By the end of the war, US factories that were dormant or nonexistent in 1941 were turning out nearly 100,000 warplanes and more than 1,000 naval and merchant ships per year.
US sees unimagined prosperity after war
The war-production boom and the draft turned a nation that had entered the war with one of the world's smallest armies into the most formidable military power on earth. With that power came global responsibilities - including containing the spread of communism - that brought an end to two centuries of US isolationism.
Economically, the labor of war obliterated high unemployment, ending the Great Depression of the 1930s virtually overnight. By war's end, full employment and a huge accumulation of private savings set the stage for an avalanche of consumer spending that would lead to rapid inflation but also to unimagined prosperity.
"The America of V-J Day was prosperous, more prosperous than the country had been in all its three centuries of zest for good living," wrote historian Eric Goldman in "The Crucial Decade: America, 1945-1955" (reprinted 1982).
Nor was prosperity confined to the upper classes. High levels of employment and the benefits bestowed by the GI Bill of Rights opened up economic, employment, housing, and educational opportunities to a vast new middle class.
"The two world wars affected the domestic society like giant leveling bulldozers," writes Mr. Goldman of the social changes wrought by prosperity.
The war also changed the future for women and blacks in the US. The transfer of millions of men from the factory to the battle front necessitated the transfer of millions of women from the home to the factory. There, they demonstrated a point that would undergird the feminist movement of the postwar years: that a woman can do "a man's work," and do it well.
The paradox of fighting for freedom abroad and returning to Jim Crow desegregation laws at home, meanwhile, catalyzed black Americans and political leaders alike, laying the groundwork for the civil rights movement.
By 1948, President Harry Truman had moved to end segregation in the US military. Within a decade the courts - and later, Congress - would reluctantly begin to champion the cause of equal rights for black Americans.
Perhaps no one knew better than Truman, who had been president for only four months on V-J Day, that the euphoria of Aug. 14 would be followed by a difficult readjustment to peacetime, replete with high inflation, labor unrest, and foreign policy crises as well as good times.
It was "a great day," he told a throng gathered in front of the White House on V-J Day. But a crisis lies ahead, he added - "as great ... as Dec. 7, 1941."