The Four Nations lived in harmony until the Fire Nation attacked. That’s when Fire Lord Sozin instigates the Hundred Year War using a comet that would come to carry his name. Sozin, having only recently left Avatar Roku to succumb to fumes at the mouth of a volcano, is aware that his next incarnation will come in the form of an Airbender. A plan starts to form, of course. He will use the comet (famous for its firebending enhancing properties) to incinerate every last Airbender and remove his greatest threat in the process. And so he waits... plots. And when the comet arrives, he carries out years worth of planning with near perfect precision. Ironically, missing only his one real target and a few other slippery Airbenders, he leaves only Aang to carry on the legacy of the Air Nomads.
Sozin’s ruthlessness all but forces the Earth Kingdom and Water Tribes to declare war on the Fire Nation. Fire Lord Sozin would spend the rest of his life searching for the Avatar and leave behind a war that would last a hundred years; the genocide of an entire nation of people. Three nations were locked desperately in combat for a century, but which nation is strong enough to come out on top in this global conflict? Will the Fire Nation come out on top?
4) The Air Nomads
The Air Nomads are not only here in last place because they are the first nation taken out by the Fire Nation, but also because of the totality in which they were taken out. Air Nomads culture comes in complete conflict with the entire idea of war. While they are pacifists by nature, they are more than willing to defend themselves and their country; as evidenced by the slew of bodies around the skeleton of Monk Gyatso.
The Air Nation is also the nation with the lowest population and smallest economy (dealing mostly in local agriculture). With four air temples across the globe, separated by gender, they are also the nation that had spread themselves the thinnest.
The four air temples were generally reserved for monks, nuns, and children, but Air Nomads of all ages would gather at the temples for spiritual events, like picking a sky bison or attending sporting events like The Sky Bison Polo Championships. The phrase “Divided we fall” comes to mind when thinking about the fate of the fun-loving and gentle air nomads.
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3) The Water Tribes
A common trait for the nations here at the bottom of the list is that these are nations divided. Both Water Tribes are completely isolated from their sister tribe. By the time Aang thaws out of his little ice bath, they’re practically separate nations. They're only really united by the common threat of the Fire Nation.
The Water Tribes are not only separated, making them an easier target than the Earth Kingdom, they are also the nation with the fewest people (after Aang’s lonely nation of one). The northern and southern Water Tribes may not have the numbers backing them, but what they do have is the moon and a near-ubiquitous supply of their native element. These benders gain prominence as the sun sets, making them powerful adversaries with the arrival of night.
Some of the most powerful among their numbers are capable of great feats of healing and even physical domination of an opponent through blood-bending. The Water Tribes may be a nation split in two, but they have kept the fight going for a hundred years. If Aang hadn’t shown up when he did, they would’ve kept it going for a hundred more.
2) The Fire Nation
Fire Lord Sozin may have started the Hundred Year War with the help of Sozin’s comet, but he certainly had no idea how to finish it. It seems like the Fire Nation’s only real plan was to rely on the power of the comet when it came around and win by the time it disappeared (or hope to last long enough to see it again).
While the Fire Nation doesn’t have to worry about the separation of its powers like the other nations, it is essentially an island nation similar to Japan. This means that in order to wage any sort of war, much less a war against every other nation, they have to send troops away from home. They are fighting for conquest, not defense. It is a war of attrition that they are losing. Even the separated water tribes are able to mount a defense against the thinly spread Fire Nation.
Firebenders are, however, powerful opponents whose native element is the only element that takes a life of its own when they finish manipulating it. Fire is fuel and life, but it is also destruction and death. The Fire Nation knows this fact and they take full advantage of it.
1) The Earth Kingdom
That’s right all you Fire Nation fanboys and girls! The Earth Kingdom’s coming out on top in this global conflict. There are a number of factors that make the Earth Kingdom the strongest nation from a militaristic standpoint. One of the big ones is just how much of the map they take up. Not only that, but they are a singular nation, connected on all ends, with reinforcements close by wherever they are needed. The Water Tribe may be known as the most fluid nation in the world of Avatar: The Last Airbender, but I’d actually argue that it is the earth that is the most malleable element.
From good ole fashioned earthbending to metalbending, even lavabending (you have to believe at least one talented earthbender was out there paving the way), earthbenders are capable of an incredible variety of tricks with their native element. It seems like Sozin let his hot-headedness control him and couldn’t see that the Earth Kingdom was made to stand the test of time.