The American Occupation had a tricky job as they saw it. On the one hand, they wanted to transition Japan from the sort of place that had massive imperial ambitions and war-mongering tendencies into a valuable American ally in the Pacific region, a buffer of sorts against Communism. On the other hand, they were going to occupy the country and run it for half a decade or so, and they had just waged a pretty nasty total war against the Japanese, and the Japanese themselves had just alienated pretty much every other nation in the region on account of said imperial ambitions and war-mongering tendencies.

The choice to allow Hirohito to remain was made by General MacArthur, who oversaw the Occupation. For MacArthur, keeping Hirohito in place, but making him essentially a figurehead, allowed him to keep a firm had on the existing Japanese bureaucracy and mandarin classes. Like most armies of occupation, but certainly ones of a temporary nature and from a foreign culture, the US Occupation sought to have the majority of the actual "work" of governance be done by the Japanese themselves, with the Americans "guiding" from the top. Keeping as much of the bureaucracy in place allowed this to work, and keeping Hirohito nominally at the top of this insured a sort of continuity. Hirohito, even in the imperial days, never managed much of the day-to-day; it was not that kind of job.

MacArthur in particular believed that the masses of the Japanese public in particular adored Hirohito, and saw their definition of Japan as being tied up with the imperial house. Preservation of this, in a form, was meant to keep them from getting restless, or from embracing even more radical departures in forms of government — like Communism. Keeping Hirohito around (even when there were those in the Japanese higher echelons who were floating the idea of his abdication) was meant to build a bridge from the Japan that was to the Japan that the Americans hoped would be.

MacArthur and others did a lot of work to convince both the American public and government that this was a good idea, and to convince the Japanese people that Hirohito was now a reformer, not some kind of puppet. It was a delicate balance, and not at all easy given the association of Hirohito with Japan's behavior during the war. But the Occupation officials saw no other serious choice, because, as one put it, "otherwise we would have nothing but chaos."

The book to read on this period is John Dower, Embracing Defeat: Japan in the Wake of World War II (Norton, 1999).