The fact that Godzilla is an avatar for the atom is a truism beyond dispute. Indeed, I think we can say there have been only a few other film characters as over-determined by history as Godzilla. The connection between a defeated imperialist Japan  and Godzilla is also without question; the monster came first as a destroyer, the natural sequel to both Washington's horrific atomic bombing of the people of Hiroshima and Nagasaki, and later U.S. atomic tests in the Pacific in the 1950s.
Over the course of many movies, Godzilla evolved from the devastator to the defender of Japan. As the island was assaulted by countless alien imperialists and monsters, Godzilla fought them off. His philosophy of war can be put succinctly as: "It was necessary to destroy the city in order to save it."
Were it not in such bad taste I would spend a few paragraphs discussing Godzilla in relation to Fukushima. After all, like other disasters of "disaster capitalism" the Fukushima crisis was prepared for in popular culture for decades.
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"Ghidrah: the three-headed monster" [Toho, 1964]
"Ghidrah" contains every popular fiction plot element except the kitchen sink. There is a plucky girl reporter, a tyro government body guard protecting an amnesiac princess from assassins, and three monsters: Rodan, Godzilla, and Mothra. [Mothra comes with charming twin fairies in telepathic communication with their Infant Island avatar.] All these people and creatures are minding their own business, pursuing their lives on earth, when a meteorite lands in the nearby mountains. From it Ghidrah emerges, a three-headed monster who has [we learn via telepathy and hypnosis when the princess' mind is taken over by a Martian] laid waste to the red planet already.
Toho and director Inoshiro Honda set themselves an ambitious task. The movie is a large social tapestry featuring poor fishermen, top cops, radio journalists, assassins and mobsters, a UFO cult, and a variety TV program. Paul Thomas Anderson's "Magnolia" may more effectively combine different characters and plot threads, but Anderson never had the courage to include as the film's pivotal scene a debate between Rodan, Godzilla, and Mothra over whether they will combine their strength to collectively defeat Ghidrah. The debate is emphatic and animated, and when all three agree to put side their distaste for humanity in order to defeat the "enemy of their enemy", they set to work with a will.
Many scenes in the film are elegantly poetic. The princess, on an airliner, communing with an alien light through the window; a pod of breaching whales foreshadowing Godzilla's rise from the ocean depths; Rodan emerging from the wall of a volcano as tourist a few feet away a is retrieving a lost hat. The energy and economy of these moments is preserved throughout the movie. One particularly tense scene, reminiscent of the idiosyncrasy of Brian De Palma in its staging, features the body guard and the assassin shooting at each other from opposite walls of a sheer and narrow valley while the monsters war beyond them. As each man shoots, he is framed head-on facing the viewer; we are given no cues to suggest how far apart they are; their guns fire like guns in dreams: small and ineffective pops not at all commensurate with the grand stakes involved.
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The makers of "Ghidrah" and the other Toho monster movies picture Japan as a society constantly beset by disaster. Government officials, on the announcement of each turn of events, rush to TV cameras to admit they are powerless. And then the biggest disaster becomes the island's saving grace: Godzilla [and often his comrades, too] thwart the bigger crisis before returning to their beds for a well-deserved rest. This view of Japan is not so different from popular sentiment in any national defeated in a way; it reaches such a height of intensity in Japan because, in addition to defeat in inter-imperialist war, it is also - as an island - the crossroads of tectonic disaster.
Only in fantasy does Japan, then, rescue itself from the jaws of defeat; Godzilla, full-blown from the brow of a defeated state, is fantasy's victory over historical reality.