system
Given the following post, respond as if you're commenting on Reddit:
human
[Avatar:TLA] What would've happened if the 100 year war was started by another nation?

Sozin's comet gave the Fire Nation the strength to destroy the Air Nomads, but what if there was a recurring tsunami or earthquake that gave the Water or Earth nations the power to invade? Or even if the Fire Nation had decided to destroy another nation instead of the Air Nomads. How different would the world be?
gpt
The earth kingdom would have successfully become the only global power, only without having to completely wipe out the other nations. They are simply too big and number too many, their weakness lies in their city-state structure of government. They simply lack the unification of the other nations, instead being broken up into very many almost independent cities. 

In a time of aggressive military action, they could unify and vastly improve their strength. But even then, the fighting would be minimal. Fire nation, despite what may seem obvious, would fall first. They rely heavily on trade from the earth kingdom, hence the massive colonization in then series. An embargo would cripple them, and without the extensive military research done during the 100 year war, they would simply lack the defenses. 

Water tribe would be useless to them (very little earth on the poles.) A direct confrontation would be suicide, siege tactics would be ineffective, and killing the moon spirit would hardly be a good idea. The only way to capture the water tribes would be to buy them. So they open up trade. Lots of it, generously. Food, artwork, textiles, gems, whales, spices. They place an artificial value on water tribe money, make it a really high exchange to earth coins, send merchants and immigrants to the poles in droves with promises of wealth. No war, just integration. Before long the north pole is nothing more than a puppet state.

The air nomads wouldn't fall. They only fell to begin with because of a freak occurrence, however they wouldn't get off easy, their cities would likes be entirely destroyed with little they could do to stop it. It  They are nomads, though, and they would be fine. All they would have to do is dissolve and return to being nomadic. They'd be fine, and the earth kingdom would consider it a victory and leave them alone.