Discovery Age is probably one of the best ways to describe Eorzea's overall world theme. In that sense, it offers something different from Vana'diel, which had a heavier emphasis on nationalism and ethnic rivalries.
I've always been fascinated with how the Final Fantasy franchise adapts real-world issues into the storylines of its games. In the case of Vana'diel, it incorporated issues as diverse as capitalistic greed (Bastok's plutocratic merchants), racial tensions (the humes' disdain for the typically working-class galka), xenophobia (the infuriating ethnic chauvinism of San d'Oria's elvaan), misplaced patriotism (the over-proud elvaan aristocracy, clinging stubbornly to fading glory) and environmental degradation (the priaries around Windhurst, slowly being wrecked by an experiment gone awry).
By the time players first enter
FFXI, Vana'diel had already undergone an entire generation of socio-cultural and political upheaval. The Crystal War that nearly destroyed all civilisation 20 years prior to the start of the game is comparable, in a way, to World War II in our reality: It marked the complete end of one way of life and the beginning of something entirely new. Vana'diel's Age of Adventurers was a time of unprecedented social mobility, as men and women of all races and nationalities mixed freely, fighting the remnants of beastmen tribes that still openly roamed the land.
To a certain extent, the airship was a symbol of the new era. The flying machines were introduced to Vana'diel shortly after the start of the Crystal War, revived by the Grand Duchy of Jeuno and improved upon by Cid, Bastok's engineer extraordinaire. The airships facilitated the crumbling of national borders and connected former rival cities together in a vast network with Jeuno, the leading power of the new world order, serving as the hub of all trade and travel.
As a young adventurer visiting each of the nations early in the game's storyline, you could immediately sense the differences in culture and political attitude between them. It gave the world a sense of history and reality, making Vana'diel feel plausible.
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Eorzea, to me, is a subtly different world because of the heavier emphasis on individual enterprise and endeavour. The continent, in a way, feels like the Africa of our world, a vast land of rich, untapped resources. The individual city-states embrace a frontiersmen-like work ethic. National pride does not appear to matter as much as individual advancement through dedication to one's chosen profession.
Overall, there also seems to be a stronger environmental theme, as all three main plots appear to hint at a major disturbance in the natural balance, thus awakening mythical creatures that threaten to bring apocalyptic ruin to the world.
And unlike Vana'diel, which had already sustained and survived a world war, Eorzea had not yet been actually invaded. The threat of attack by the Garlean Empire, with its superior technology such as airships and apparently advanced firearms, is always looming in the background. But, as hinted in FFXIV's opening movie, the imperial forces appear to be kept at bay, for the time being, by primal forces. What those primal forces may be, the player-adventurers will probably one day discover as they delve deeper into the game's plot.