Based on a lot of the political/historical/mythological references, I would say it goes something like this:
Fire Nation = Japan. The country itself is a chain of islands, and the way their justification for the war being to share the greatness of their superiority with everyone is a direct reference to Japan's so-called Greater East Asia Co-Prosperity Sphere of the 1940s. Plus, you have the Fire Nation's ties to the sun, whose patron Goddess, Amaterasu, is the principal deity of Japanese mythology.
Earth Kingdom = China. They're the largest country of the Avatar world, and Ba Sing Se is the spitting image of the Forbidden City. The Dai Li themselves are named for the head of Chiang Kai-Shek's secret police, who operated much like their namesakes. And the Earth King is a huge reference to Pu Yi, the head of Japan's puppet government during the occupation of northern China in the 1920s.
Air Nomads = Tibetans. Gyatso, Aang's mentor, was likely named for Palden Gyatso, a Tibetan monk who led the first Tibetan uprising when the country fell under Chinese rule in 1958.
Water Tribes = Inuit. Directly stated in numerous DVD extras, and rather obvious by their dress and locales.
Re: 6, 8, 15, 35
Fire Nation = Japan. The country itself is a chain of islands, and the way their justification for the war being to share the greatness of their superiority with everyone is a direct reference to Japan's so-called Greater East Asia Co-Prosperity Sphere of the 1940s. Plus, you have the Fire Nation's ties to the sun, whose patron Goddess, Amaterasu, is the principal deity of Japanese mythology.
Earth Kingdom = China. They're the largest country of the Avatar world, and Ba Sing Se is the spitting image of the Forbidden City. The Dai Li themselves are named for the head of Chiang Kai-Shek's secret police, who operated much like their namesakes. And the Earth King is a huge reference to Pu Yi, the head of Japan's puppet government during the occupation of northern China in the 1920s.
Air Nomads = Tibetans. Gyatso, Aang's mentor, was likely named for Palden Gyatso, a Tibetan monk who led the first Tibetan uprising when the country fell under Chinese rule in 1958.
Water Tribes = Inuit. Directly stated in numerous DVD extras, and rather obvious by their dress and locales.