U.S. Gen. Douglas MacArthur, left, with Japanese Emperor Hirohito, Sept. 27, 1945.

After achieving victory in World War II, the United States found itself in a dilemma. Its vanquished adversaries, Germany and Japan, both lay in ruins. But America's wartime ally of expedience, the Soviet Union, quickly had emerged as a dangerous rival. The Soviet Army occupied the eastern half of Germany, and on the other side of the globe, the United States feared the rise of well-organized Japanese communists who might push that nation into the Soviet orbit.

In response, the United States took a drastically different approach from the Allies' harshly punitive handling of Germany after World War I. Under President Harry Truman, the U.S. strategy was to rebuild the economies of both former enemies and establish stable parliamentary democracies. The result was what Carnegie Endowment for International Peace scholar Matina Ottaway has called "the most successful nation-building exercise ever undertaken from the outside."

In Germany, the job was particularly complicated, since the United States and its allies controlled only the western portion of the country, and half of the divided city of Berlin in East Germany. Nevertheless, the nation-building effort was breathtakingly rapid. Instead of zealously rooting out anyone who'd been connected with the Nazi regime, the occupiers put a few top leaders on trial and let everyone else go back to work.

They allowed old political parties from the pre-Nazi days to form again, and replaced the worthless, hyper-inflated Nazi-era money with a new currency, the Deutsche mark, so that prices stabilized and consumer goods again became available and affordable. In 1949, they allowed delegates from elected local governments to write a constitution (which the occupiers approved) and form the Federal Republic of Germany. By the mid-1950s, West Germany had become such a trusted U.S. ally that it was even allowed to arm itself.

In Japan, the U.S. military government, headed by Gen. Douglas MacArthur, didn't engage in nation-building so much as it did nation-modifying. The Americans adroitly utilized the Japanese population's paradoxical combination of loyalty to its traditional institutions and resentment against the right-wing militarist leaders who'd led the nation into a debacle.

MacArthur made a show of putting a few of those unpopular leaders on trial, but allowed Emperor Hirohito to stay on the throne as ceremonial ruler of the new constitutional democracy, even though he personally had approved the attack on Pearl Harbor. Hirohito instead became a useful public-relations tool for the occupiers. When a photograph of the diminutive Hirohito standing stiffly at attention next to the burly, 6-foot-4-inch MacArthur ran in Japanese newspapers, it sent out a powerful message about who was in charge.

Initially, the Americans tried to break up the system of giant, family controlled conglomerates that monopolized the Japanese economy, but then allowed it to return as a way to thwart the rising power of labor unions and radical students. Ultimately, many of the old right-wing, militarist leaders who had been accused of major war crimes were freed and allowed to return to public life.

In 1950, the Korean War finally provided Japan's economy with a desperately needed jolt. The Pentagon bought supplies from the Japanese, and utilized the factories and skilled workers who'd built the Japanese war machine to repair American tanks and planes. Those procurements pumped billions of dollars into the Japanese economy. By the time the occupation ended in 1952, the Japanese economy was well on the way to recovery.