All art is derivative in some way, and this is no different for Avatar: The Last Airbender; creators Bryan Konietzko and Mike DiMartino have spoken many times about the wide spectrum of material used to weave the series' intricate narrative. The duo has discussed the heavy influences taken from cultures of South and East Asia, Africa and First Nations as well as their tendency to turn to real-world historical ideology, like Buddhist anarchy and militant fascism, to develop conflict within the series.
This combination of cultural and historical influence is what allows the creators to craft a story in ATLA that simultaneously feels both fantastic and familiar. Konietzko and DiMartino incorporate elements from various real-world conflicts into the story of ATLA in order to create the perfectly detestable antagonist, the Fire Nation. ATLA presents audiences with a gravely threatening enemy, but without alienating its own young key demographic, by borrowing from the tragedies of real historical wars that speak to today's understanding of modern society.
The Hundred Years' War
ATLA's most blatant references to history come in the way of interesting nods toward the relatively brief European conflict known as the Hundred Years' War. This series of battles between Britain and France lasted from 1337 to 1453, having long-lasting impacts that would be echoed within the Avatar franchise.
The duo chooses an on-the-nose approach toward evoking the Hundred Years' War, as the citizens of ATLA's four nations refer to the Fire Nation's onslaught as the "Hundred Year War." Moreover, the two creators seem to have been interested in more than the name, as the timeframe and structure of ATLA's world conflict mirror those of the Hundred Years' War, i.e. a century-long series of escalating armed conflicts interrupted by periods of respite.
The Second Sino-Japanese War
Beyond aesthetic homages, the creative duo does an excellent job at utilizing the Fire Nation as a proxy to portray the complexities of Japanese culture and history. ATLA's most significant motif, that of "honor," is clearly meant to mirror the historical significance of chivalrous or honorable values within Japanese culture, often understood as the "Bushido Code" in the West.
Through the Heel-Face Turn protagonist Prince Zuko, audiences are able to understand how the Fire Nation's cultural emphasis on honor can motivate one to heroic action -- a common theme across historical portrayals of pre-Meiji Japan. Similarly, Konietzko and DiMartino illustrate the Fire Nation's terror by mirroring more radical demonstrations of historic Japan's "honor-value" culture, i.e. the Second Sino-Japanese War's Nanjing Massacre.
As Phoenix King Ozai invades China's fictional proxy, the Earth Kingdom, the flame supremacist moves beyond conquering the land by incinerating everything in sight with the goal of "destroying the precious hope" of the people. In the same way, Axis-era Japan attempted to destroy the "honor" of an unrelenting China by repeatedly committing the worst crimes against the women and children of the nation's former capital, Nanjing.
At the end of ATLA's Hundred Year War, Ozai is sentenced and imprisoned for the severity of his war crimes, again highlighting the impact that the Nanjing Massacre had on the series' epic finale. That is to say, Ozai's fate echoes the fate of Japanese Imperialist Iwane Matsui, who was tried, imprisoned and executed for the gravity of his war crimes against China years after leading his forces during that six-week onslaught on the honor and hope of Chinese civilians.
World War II
The scars of World War II are fresh enough within the collective consciousness that it's still difficult to find media that does not harken back to the historical accounts of that era in some way, and ATLA is no exception. In fact, the entirety of the series' chronic conflict, i.e. an aggressive Fire Nation unbalancing the world due to a sense of supremacy, resembles the fascist attitudes and actions of WWII's aforementioned Axis Powers.
The Fire Nation's goals -- to destroy the culture and lands of their enemies and forcefully assimilate the world under their supreme ideology -- are by definition a facsimile for the fascist ideologies that were popularized in mid-20th-century Europe. Through the self-proclaimed ruler of the world, Ozai, the audience is introduced to the historically charismatic dictator that movements like these are often centralized around.
Beyond wartime actions and ideologies, the Mechanist's invention and the Fire Nation's appropriation of the war balloon from Episode 17 mimics the heavy usage of war balloons throughout WWII by both Allies and Axis Powers. Similarly, Sokka's invention of the waterbending-powered submarine in Episode 50 is a direct parallel to the employment of Higgins Boats for amphibious landings during WWII.
As Netflix develops a new live-action addition to the franchise, it's clear that ATLA continues to speak to deeper sentiments than many give the series credit for. With its foundation rooted in the raw reality of no less than three historical conflicts, Aang's story is sure to hold its spot in modern culture.