The monster, Cohen tells us, exists only at its cultural moment and therefore exists only as an embodiment of that cultural moment. The monster you read (or watch or listen to) exists only to be read (or watched or listened to), and so we have a monster designed to entirely embody that time, feeling, and place of its moment within its culture. It is unsurprising, then, that the physical body of the monster itself is made up of the fears, desires, anxieties, and fantasies of, again, the cultural moment.
The cultural moment from which ATLA was born is still recent, barely history, and we can see the desires of a world rapidly globalizing: take Appa, whose body itself transports our heroes far and wide, easily across the world. We can see the fears – a show created for a world that has seen two World Wars and aimed at a generation who largely remembers 9/11 but not the world before it – the Fire Nation as monstrous fits the cultural moment. We understand why fire is the element we are most afraid of, having watched buildings burn from all over the world, and we understand a world afraid of the power of nations and fascism and military strength.
But if the monster is coded as cultural, this can be subverted so that the monster is used to create a sense of culture… pick your nation: