About thirty-five years prior to the Hundred Year War, the ambitious Fire LordSozin began to dream of a global empire where he would unite the four nations under Fire Nation domination. It was intended to be a prosperous unity that would "share" the wealth and success the Fire Nation was enjoying during Sozin's rule. As time went on, Sozin's desire for world domination grew drastically, and his rule became increasingly dictatorial. AvatarRoku warned his long-time friend to not expand the Fire Nation, as the four nations were meant to be just four. However, Sozin disregarded Roku's warning and put his plans into motion by invading and successfully occupying Earth Kingdom territory. This first assault was short-lived; when Roku discovered the existence of the numerous Fire Nation colonies in foreign lands, he confronted Sozin about his course of action. The Avatar swiftly defeated the Fire Lord, though let him go in the name of their past friendship with a final warning that he would end his former friend's life if he continued his invasion plans. However, these first colonies, especially Yu Dao, remained in the Earth Kingdom, growing and prospering during the following decades.
For twenty-five years, the world was at peace again, until a volcanic eruption brought an end to Roku's life to which Sozin realized his visions for the future were suddenly possible again. Sozin waited twelve years after Roku's death for the return of the Great Comet to commence his invasion of the other nations. He launched an attack on the Air Nomads, the native nation of the next Avatar, causing their extermination and instigating the century-long war.
After the Air Nomad Genocide, Sozin focused his attention on the Earth Kingdom. Many colonies were established across the continent, and their population steadily increased due to aggressive efforts in forcing citizens to leave for the Earth Kingdom. As Fire Nation forces encroached the Earth Kingdom's numerous territories, these colonies grew into prosperous settlements and supported the Fire Nation's war effort through the supplement of food and war supplies.
Dozens of these colonies were established across the Earth Kingdom continent. Like most of the population back home, these Fire Nation citizens supported the war effort, and were fed with the various forms of propaganda used to instill support with the front line troops. They often took advantage of living in the prosperous Earth Kingdom by depriving the indigenous of their resources and making them work on their behalf.
After the Hundred Year War ended, Zuko was crowned the new Fire Lord, and he announced an era of peace to begin, in which he would strive to restore the honor of the Fire Nation.
In order to restore peace and balance in the world, the Harmony Restoration Movement was launched with the aim of transferring the Fire Nation colonials back to their home nation. However, a year after the Hundred Year War's conclusion, new disputes arose over the existence of the colonies on Earth Kingdom territory and ignited fresh tensions with the Fire Nation, threatening to devolve into war between the two countries and civil war within the Fire Nation itself. The resulting outcry necessitated the intervention of Team Avatar on behalf of Fire Lord Zuko. Realizing that the conflict could never be truly solved, as the colonials were no longer Earth Kingdom and Fire Nation divided, though rather a new people, Avatar Aang and Fire Lord Zuko abandoned the Harmony Restoration Movement and transformed the colonies into the United Republic of Nations.
The culture of the Fire Nation colonies was very much like that of the homeland. Its inhabitants celebrated various cultural festivals, supported the war effort, were indoctrinated with government propaganda, and consumed traditional Fire Nation cuisine. Regardless of their ties to the homeland, these colonials were often belittled with disdain by citizens from the Fire Nation archipelago, which commonly resulted in unequal treatment. However, the culture was less tightly regulated than in the Fire Nation proper and as a result, colonists had slightly greater freedom of expression, and were permitted to dance. Despite these liberties, they were often unhappy with the state of their lives.
In many colonies, namely Yu Dao, social discrepancies between Fire Nation citizens and Earth Kingdom natives were widespread. Usually, Earth Kingdom citizens would occupy a second-class position in the city's society, while the higher positions were generally reserved for the Fire Nation residents. This social division led in many cases to an inequality in wealth among the citizens, leaving some people at the mercy and submission of the nobility's power.
In older colonies, the union between the settlers and locals became natural, giving rise to a new race of mixed Fire Nation and Earth Kingdom origin. People from different races often worked together in hopes of being more productive. The formation of families among people of different origins thus became one of the causes of the Harmony Restoration Movement's intermission to assess these situations in the colonies.